OChem1 Course Pack Practice Exams Practice Problems by Chapter Mechanism Flashcards

Transcription

1 Chem1 Course Pack Practice Exams Practice Problems by Chapter Mechanism Flashcards

2 Chem1 Practice Exams Dr. Peter Norris, 2014

3 Chemistry 3719 Practice Exam A1 This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (8 pts) Draw structures for all of the cycloalkane isomers with the formula C 5 10, and then give each of your structures an acceptable name. (Klein Chapter 4) 1

4 2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or common names for substituents. (Klein Chapter 4) a. C 3 C 2 C 3 b. c. 3. (8 pts) Fill in the ground state electron distribution for (from the periodic table), and then construct hybrid orbital pictures for the highlighted atoms that describe the orbitals used for bonding in each case. (Klein Chapter 1) Explain briefly why hybrid orbitals are necessary here: 2

5 4. (12 pts) Give the products expected from each of the following acid-base reactions. Then label each acid with an approximate pk a and indicate whether products, reactants, or neither are favoured in each case. (Klein Chapter 3) a. C 2 + C 3 C 2 K b. C C + LiN[C(C 3 ) 2 ] c. + C 3 Na 5. (8 pts) Give the three acids below an approximate pka value and then explain why they have such different acid strengths even though they each have an group as the acidic component. (Klein Chapter 3) 3

6 6. (6 pts) Complete the following structures by adding any needed formal charges. (Klein Chapter 2) 7. (6 pts) Draw a second resonance structure and an overall hybrid for each of the following species. (Klein Chapter 2) a. 3 C b. C N N c. C 3 C 2 8. (6 pts) For the three molecules below, discuss their relative solubilities in aqueous solution in terms of the forces that are playing a role here. (Klein Chapter 1) 4

7 9. (10 pts) Draw two chair conformations for cis-1-t-butyl-3-methylcyclohexane that are related through a ring-flip. Then circle which conformation you expect to be more stable and explain why. Then do the same for the trans isomer and, finally, indicate whether the cis or trans isomer should be more stable overall and explain your choice. (Klein Chapter 4) 10. (9 pts) Draw Newman depictions that correspond to the following conformations. (Klein Chapter 4) a. The least stable conformation of 3-methylnonane along the C-4 C-5 bond. b. The most stable conformation of 1,1-dibromo-6-chlorohexane along the C-3 C-4 bond. c. A gauche conformation for 5-methyl-2-heptanol along the C-3 C-4 bond. 5

8 11. (9 pts) Rank the following species as indicated: (Klein Chapters 1-3) a. Lowest to highest electronegativity (1 = lowest, 5 = highest) b. Lowest to highest pka (1 = lowest, 5 = highest) c. Lowest to highest boiling point (1 = lowest, 5 = highest) 12. (9 pts) Within each pair of molecules below, indicate which is more stable and then give a brief explanation for your choices in each case. (Klein Chapters 3-4) a. Na vs. Na b. vs. c. Li vs. NLi 6

9 Chemistry 3719 Practice Exam A1 Key This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (8 pts) Draw structures for all of the cycloalkane isomers with the formula C 5 10, and then give each of your structures an acceptable name. (Klein, Chapter 4) 1

10 2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or common names for substituents. (Klein Chapter 4) C 3 a. 5-ethyl-1-isopropyl-2-methyl-3-propylcyclohexane C 2 C 3 b. 5-isopropyl-2,6,7-trimethylnonane c. bicyclo[4.3.1]decane 3. (8 pts) Fill in the ground state electron distribution for (from the periodic table), and then construct hybrid orbital pictures for the highlighted atoms that describe the orbitals used for bonding in each case. (Klein Chapter 1) Explain briefly why hybrid orbitals are necessary here: The most obvious reason is that the lone pairs in the ground state structure of xygen are not equivalent; the hybridization model fixes that. 2

11 4. (12 pts) Give the products expected from each of the following acid-base reactions. Then label each acid with an approximate pk a and indicate whether products, reactants, or neither are favoured in each case. (Klein Chapter 3) a. C 2 + C 3 C 2 K C 2 K + C 3 C 2 pka~5 products f avoured pka~16 b. C C + LiN[C(C 3 ) 2 ] C C Li + N[C(C 3 ) 2 ] pka~26 products f avoured pka~38 Na c. + C 3 Na + C 3 pka~16 neitherfavoured pka~16 5. (8 pts) Give the three acids below an approximate pka value and then explain why they have such different acid strengths even though they each have an group as the acidic component. (Klein Chapter 3) The first molecule has pka = 16 since it is an alcohol, the second has pka ~5 since it is a carboxylic acid, and the third has pka = 10 since it is a phenol. The difference in pka values is down to the relative stabilities of the conjugate bases formed from each; the first compound produces an anion in which the charge is localized on and therefore unstable. The carboxylic acid produces a conjugate base in which the charge is delocalized onto two atoms, which is quite stable. The third molecule also has a resonance-stabilized conjugate base, however here the charge is delocalized into and C, which isn t as favourable as the carboxylate situation. The more stable the conjugate base, the more acidic the associated acid. 3

12 6. (6 pts) Complete the following structures by adding any needed formal charges. (Klein Chapter 2) 7. (6 pts) Draw a second resonance structure and an overall hybrid for each of the following species. (Klein Chapter 2) 8. (6 pts) For the three molecules below, discuss their relative solubilities in aqueous solution in terms of the forces that are playing a role here. (Klein Chapter 1) Molecule A will be the least soluble in water since although features a hydrogen-bonding alcohol it also has a hyprophobic alkyl chain that will repel water. Molecule B has a shorter alkyl chain so the group will have more of a role than in A and increase water solubility. Molecule C should be the most soluble since it is ionic. 4

13 9. (10 pts) Draw two chair conformations for cis-1-t-butyl-3-methylcyclohexane that are related through a ring-flip. Then circle which conformation you expect to be more stable and explain why. Then do the same for the trans isomer and, finally, indicate whether the cis or trans isomer should be more stable overall and explain your choice. (Klein Chapter 4) 10. (9 pts) Draw Newman depictions that correspond to the following conformations. (Klein Chapter 4) a. The least stable conformation of 3-methylnonane along the C-4 C-5 bond. b. The most stable conformation of 1,1-dibromo-6-chlorohexane along the C-3 C-4 bond. c. A gauche conformation for 5-methyl-2-heptanol along the C-3 C-4 bond. 5

14 11. (9 pts) Rank the following species as indicated: (Klein Chapters 1-3) a. Lowest to highest electronegativity (1 = lowest, 5 = highest) b. Lowest to highest pka (1 = lowest, 5 = highest) c. Lowest to highest boiling point (1 = lowest, 5 = highest) (9 pts) Within each pair of molecules below, indicate which is more stable and then give a brief explanation for your choices in each case. (Klein Chapters 3-4) 6

15 Chemistry 3719 Practice Exam A2 This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (9 pts) For each of the following pairs of molecules, provide the configuration of each chiral centre and then indicate whether the two molecules within a pair are enantiomers, diastereomers, or are identical. (Klein Chapter 5) a. and C 3 C 3 b. C 3 and C 3 C 3 C 3 c. C 2 Cl C 3 F and 3 C F C 2 Cl 1

16 2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or common names for substituents. (Klein Chapters 7-8) a. F F b. c. Cl I 3. (8 pts) Provide a detailed mechanism for the following transformation that uses curved arrows to show the breaking and forming of bonds. Explain why this product is the major product formed. (Klein Chapter 8) 2

17 4. (8 pts) The following solvolysis conditions give two major products in equal amounts but, when measured for the mixture, [α] D 0. Provide the products and a mechanism for this process, as well as an explanation for the optical rotation data. (Klein Chapter 7) 5. (8 pts) The following reactions have only slight differences; however the ratio of products formed in each case is dramatically different. Provide a detailed mechanistic explanation for this data. (Klein Chapter 8) 6. (6 pts) Rank the following in decreasing order of reaction rate in S N 1 with (4 = fastest, 1 = slowest) and then give a brief explanation for your choices. (Klein Chapter 7) 3

18 7. (10 pts) n the axes given below, draw a complete reaction profile for the following reaction that includes diagrams of all intermediates and transition states involved. (Klein Chapters 6-7) NaCl P.E. Cl reaction coordinate 8. (8 pts) Give the major products expected from each step in the following synthetic sequence. Be careful to take into account any stereochemical issues along the way. (Klein Chapter 7) 4

19 9. (15 pts) Give the expected products, major and minor where applicable, in each of the following situations. Be sure to take into account any changes in stereochemistry that may occur. (Klein Chapters 7-8) a. 3 C 1. S 2 Cl pyridine 2. NaCN, DMF b. 2 S 4, heat c. I C 3 d. NaC 3, DMF e. C 2 I NaN 3, DMS C 3 5

20 10. (8 pts) Give a mechanism for the following reaction using curved arrows to describe all bond-forming and breaking events. Then draw a transition state for the R.D.S. and explain why this is the major product. (Klein Chapter 8) 11. (6 pts) Convert the following stereochemical representations as directed. Working out R/S configurations might help but are not required as part of the answer. (Klein Chapter 5) 12. (5 pts) Dehydration of a tertiary alcohol in the presence of catalytic acid through the E1 pathway is thermodynamically unfavourable since sigma bonds are swapped for a pi bond. Explain how this process is made viable such that the alkene is able to be formed and isolated in high yield. (Klein Chapter 8) 6

21 Chemistry 3719 Practice Exam A2 Key This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (9 pts) For each of the following pairs of molecules, provide the configuration of each chiral centre and then indicate whether the two molecules within a pair are enantiomers, diastereomers, or are identical. (Klein Chapter 5) 1

22 2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or common names for substituents. (Klein Chapters 7-8) 3. (8 pts) Provide a detailed mechanism for the following transformation that uses curved arrows to show the breaking and forming of bonds. Explain why this product is the major product formed. (Klein Chapter 8) The secondary carbocation that is formed undergoes rearrangement to produce a better tertiary cation that no longer has the strained cyclobutyl ring involved. The tertiary carbocation is then deprotonated to give the most highly substituted alkene which is stabilized by four electron-donating alkyl groups through inductive effects. 2

23 4. (8 pts) The following solvolysis conditions give two major products in equal amounts but, when measured for the mixture, [α] D 0. Provide the products and a mechanism for this process, as well as an explanation for the optical rotation data. (Klein Chapter 7) 5. (8 pts) The following reactions have only slight differences; however the ratio of products formed in each case is dramatically different. Provide a detailed mechanistic explanation for this data. (Klein Chapter 8) 6. (6 pts) Rank the following in decreasing order of reaction rate in S N 1 with (4 = fastest, 1 = slowest) and then give a brief explanation for your choices. The better the possible carbocation, the faster the S N 1 reaction; 3 > 2 > 1 > C 3 3

24 7. (10 pts) n the axes given below, draw a complete reaction profile for the following reaction that includes diagrams of all intermediates and transition states involved. (Klein Chapter 7) NaCl P.E. A B C A = Cl + - B = + + C = + Cl - Cl reaction coordinate 8. (8 pts) Give the major products expected from each step in the following synthetic sequence. Be careful to take into account any stereochemical issues along the way. (Klein Chapter 7) 4

25 9. (15 pts) Give the expected products, major and minor where applicable, in each of the following situations. Be sure to take into account any changes in stereochemistry that may occur. (Klein Chapters 7-8) a. 3 C S 2 Cl Ts CN 1. pyridine NaCN, DMF S N 2 - inversion b. 2 S 4, heat E1 - Zaitsev outcome c. I C 3 C 3 + C 3 S N 1 - racemic d. NaC 3, DMF C S N 2 - inversion E2 e. C 2 I NaN 3, DMS N 3 C 2 C 3 C 3 S N 2 - inversion 5

26 10. (8 pts) Give a mechanism for the following reaction using curved arrows to describe all bond-forming and breaking events. Then draw a transition state for the R.D.S. and explain why this is the major product. (Klein Chapter 8) NaC 2 C 3 E2 C 2 C C 2 C 3 The major product is the most highly-substituted and stabilized alkene (tetrasubstituted) 11. (6 pts) (6 pts) Convert the following stereochemical representations as directed. Working out R/S configurations might help but are not required as part of the answer. (Klein Chapter 5) 12. (5 pts) Dehydration of a tertiary alcohol in the presence of catalytic acid through the E1 pathway is thermodynamically unfavourable since sigma bonds are swapped for a pi bond. Explain how this process is made viable such that the alkene is able to be formed and isolated in high yield. (Klein Chapter 8) Run the reaction at high temperature to increase the contribution of entropy to the overall free energy of the system ( G = T S) since the reaction is entropically favoured (1 mole of alcohol produces two moles of product; alkene and water). igh temperature also allows the more volatile alkene to be removed by distillation which will then force the equilibrium towards product to compensate. 6

27 Chemistry 3719 Practice Exam A3 This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (9 pts) Within each of the following pairs of molecules, indicate which will react at a faster rate in the given reaction; then give a brief explanation for your choice in each case. (Klein Chapters 7-9) a. 3 C C 3 or C 3 in electrophilic addition b. or D D in E2 elimination c. or ins N 2substitution 1

28 2. (9 pts) Give each of the following organic molecules an acceptable name using any systematic or common names for substituents where appropriate. Be sure to include stereochemical designators where needed. (Klein Chapteres 5-10) a. F b. Cl F c. C 3 3. (9 pts) For the following conversion, provide a detailed mechanism for the first operation only (i.e. reaction of the alkene with 3 ) that uses curved arrows to show the breaking and forming of bonds. (Klein Chapter 9) 2

29 4. (15 pts) Give the ultimate major product expected in each of the following situations. (Klein Chapters 9-11) a Zn, 2 b. 2,heat c. C 3 C 3 d. 2 in 2 e. C 3 C 3 2,Pd 3

30 5. (9 pts) Provide the major product expected under the following reaction conditions, and then give a detailed mechanism (using curved arrows) that describes its formation. (Klein Chapter 10) 6. (9 pts) Show the major product expected under the following reaction conditions, name that product, and then give a detailed mechanism (using curved arrows) that describes its formation. (Klein Chapter 11) 4

31 7. (8 pts) The following conditions induce a free radical halogenation process at the allylic position with only two products forming with a combined [α] D = 0; give a mechanistic explanation for this observation. (Klein Chapter 11) 8. (8 pts) Provide the major product expected under the following conditions and then a detailed mechanism for its formation that includes all steps that lead to this product. (Klein Chapter 11) 9. (6 pts) Provide the reagents required to complete the following transformations. (Klein Chapter 9) 5

32 10. (8 pts) The following hydroboration-oxidation sequence results in the alkylborane and alcohol shown below. Explain how the regiochemical and stereochemical outcomes help determine the mechanism in each step. (Klein Chapter 9) 11. (10 pts) n the axes given below, draw a complete reaction profile for the following reaction that includes diagrams of all intermediates and transition states involved. (Klein Chapter 9) P.E. 6 reaction coordinate

33 Chemistry 3719 Practice Exam A3 Key This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (9 pts) Within each of the following pairs of molecules, indicate which will react at a faster rate in the given reaction; then give a brief explanation for your choice in each case. (Klein Chapters 7-9) 1

34 2. (9 pts) Give each of the following organic molecules an acceptable name using any systematic or common names for substituents where appropriate. Be sure to include stereochemical designators where needed. (Klein Chapteres 5-10) a. (3R,6S)-6-fluoro-7-methyloct-4-yn-3-ol F b. Cl (R,Z)-2-bromo-5-chloro-6-methylhept-2-ene F c. C 3 (1S,3R)-3-fluoro-5-methylcyclohept-4-enol 3. (9 pts) For the following conversion, provide a detailed mechanism for the first operation only (i.e. reaction of the alkene with 3 ) that uses curved arrows to show the breaking and forming of bonds. (Klein Chapter 9) 2

35 4. (15 pts) Give the ultimate major product expected in each of the following situations. (Klein Chapters 9-11) a Zn, 2 b. 2,heat c. C 3 C 3 d. 2 in 2 e. C 3 2,Pd C 3 C 3 C 3 3

36 5. (9 pts) Provide the major product expected under the following reaction conditions, and then give a detailed mechanism (using curved arrows) that describes its formation. (Klein Chapter 10) 6. (9 pts) Show the major product expected under the following reaction conditions, name that product, and then give a detailed mechanism (using curved arrows) that describes its formation. (Klein Chapter 11) 4

37 7. (8 pts) The following conditions induce a free radical halogenation process at the allylic position with only two products forming with a combined [α] D = 0; give a mechanistic explanation for this observation. (Klein Chapter 11) 8. (8 pts) Provide the major product expected under the following conditions and then a detailed mechanism for its formation that includes all steps that lead to this product. (Klein Chapter 11) 9. (6 pts) Provide the reagents required to complete the following transformations. (Klein Chapter 9) 5

38 10. (8 pts) The following hydroboration-oxidation sequence results in the alkylborane and alcohol shown below. Explain how the regiochemical and stereochemical outcomes help determine the mechanism in each step. (Klein Chapter 9) The first step involves regioselective addition of the borane reagent such that the larger substituent on the alkene avoids the large bicyclic framework on boron; the oxidation step results in stereochemical retention, which is only possible with a concerted migration step. 11. (10 pts) n the axes given below, draw a complete reaction profile for the following reaction that includes diagrams of all intermediates and transition states involved. (Klein Chapter 9) P.E. A B C A= + - B= + + C= + - reaction coordinate 6

39 Chemistry 3719 Practice Exam B1 This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (8 pts) Fill in the ground state electron distribution for N (from the periodic table), then construct hybrid orbital pictures for the highlighted N atoms that describe the orbitals used by N for bonding in each case. (Klein Chapter 1) 1

40 2. (20 pts) For each of the following acid-base reactions, draw the conjugate acid and conjugate base that are expected to be formed. Label the acids on each side of the equations with approximate pka values, and indicate in each case if you expect the reaction to favour the left-hand side, the right-hand side, or neither. (Klein Chapter 3) a) + Na b) CF 3 C 2 K + C 3 C 2 c) N + KN 2 d) NLi + C C e) Li + 2

41 3. (15 pts) Provide acceptable names for the following molecules. Trivial or IUPAC names may be used as appropriate. (Klein Chapter 4) a) C 3 C 2 C 3 3 C C 3 b) C 2 C(C 3 ) 2 c) d) e) 3

42 4. (6 pts) Draw all of the isomeric alkanes that have the molecular formula C 5 12 and give each of them a suitable name. (Klein Chapter 4) 5. (6 pts) Provide any missing formal charges that are necessary in the following molecules. (Klein Chapter 1) a. b. c. 6. (9 pts) Draw a second resonance structure for each of the following and indicate which structure you expect to be more significant in each system. Be sure to put lone pairs in the correct places. (Klein Chapter 2) a. 3 C N b. c. S C 3 4

43 7. (10 pts) For cis-1-t-butyl-2-methylcyclohexane and trans-1-t-butyl-2-methylcyclohexane, draw two ringflipped chair forms for each isomer, then indicate the preferred conformation for each of the two isomers, and finally indicate which if the two isomers is more stable. Explain your choices in terms of the steric interactions that both isomers will experience in their respective chair conformations. (Klein Chapter 4) 8. (10 pts) Draw structures that match the following situations: (Klein Chapter 4) a) Newman projection of the least stable conformation of dodecane along the C-4 C-5 bond axis. b) Newman projection of the most stable conformation of 2-methylheptane along C-3 C-4. 5

44 9. (8 pts) In the following questions, one of the two species is less stable than the other. Indicate which is less stable in each case and explain the reason for the decreased stability. (Klein Chapter 4) 10. (8 pts) Indicate which of the following molecules should be soluble in water and which will not be soluble. iefly explain your choices. (Klein Chapter 1) 6

45 Chemistry 3719 Practice Exam B1 Key This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (8 pts) Fill in the ground state electron distribution for N (from the periodic table), then construct hybrid orbital pictures for the highlighted N atoms that describe the orbitals used by N for bonding in each case. (Klein Chapter 1) 1

46 2. (20 pts) For each of the following acid-base reactions, draw the conjugate acid and conjugate base that are expected to be formed. Label the acids on each side of the equations with approximate pka values, and indicate in each case if you expect the reaction to favor the left-hand side, the right-hand side, or neither. (Klein Chapter 3) a) + Na Na + 2 pka ~ 10 R..S favored pka ~ 16 b) CF 3 C 2 K + C 3 C 2 CF 3 C 2 + C 3 C 2 K pka ~ 16 L..S favored pka < 16 c) N + KN 2 K N + N 3 pka ~ 38 neither favored pka ~ 38 d) NLi + C C N + C C Li pka ~ 25 R..S favored pka ~ 38 e) Li + + Li pka ~ 5 R..S favored pka ~ 16 2

47 3. (15 pts) Provide acceptable names for the following molecules. Trivial or IUPAC names may be used as appropriate. (Klein Chapter 4) a) 3 C C 3 C 2 C 3 C 3 2,3-dimethylpentane b) C 2 C(C 3 ) 2 trans-1-isobutyl-3-isopropylcyclohexanol c) 3,4,6-trimethylnonane d) Bicyclo[4.2.1]nonane e) 1-(sec-butyl)-4-cyclobutyl-2-methylcyclopentane 3

48 4. (6 pts) Draw all of the isomeric alkanes that have the molecular formula C 5 12 and give each of them a suitable name. (Klein Chapter 4) 5. (6 pts) Provide any missing formal charges that are necessary in the following molecules. (Klein Chapter 1) a. b. c. N 6. (9 pts) Draw a second resonance structure for each of the following and indicate which structure you expect to be more significant in each system. Be sure to put lone pairs in the correct places. (Klein Chapter 2) 4

49 7. (10 pts) For cis-1-t-butyl-2-methylcyclohexane and trans-1-t-butyl-2-methylcyclohexane, draw two ringflipped chair forms for each isomer, then indicate the preferred conformation for each of the two isomers, and finally indicate which if the two isomers is more stable. Explain your choices in terms of the steric interactions that both isomers will experience in their respective chair conformations. (Klein Chapter 4) The trans isomer will be more stable since both of the large groups are able to be equatorial thus avoiding any destabilizing 1,3-diaxial interactions. Both of the conformations of the cis isomer will have a large group in an axial position. 8. (10 pts) Draw structures that match the following situations: (Klein Chapter 4) a) Newman projection of the least stable conformation of dodecane along the C-4 C-5 bond axis. b) Newman projection of the most stable conformation of 2-methylheptane along C-3 C-4. 5

50 9. (8 pts) In the following questions, one of the two species is less stable than the other. Indicate which is less stable in each case and explain the reason for the decreased stability. (Klein Chapter 4) 10. (8 pts) Indicate which of the following molecules should be soluble in water and which will not be soluble. iefly explain your choices. (Klein Chapter 1) Solubility is based on interactions between the solute and solvent and is generalized by the term like dissolve like here the groups are capable of hydrogen bonding with water while the hydrophobic alkyl groups will repel. Large alkyl portions outweigh the importance of the group and cause insolubility as listed; many groups (bottom left) will enhance solubility. 6

51 Chemistry 3719 Practice Exam B2 This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (8 pts) Provide a detailed mechanism, using curved arrows to show the breaking and forming of bonds, that accounts for the following conversion. (Klein Chapter 8) 1

52 2. (12 pts) Provide structures of the major and minor organic product(s) that are expected to be formed in each of the following situations. (Klein Chapters 7-8) a) NaC 3 b) C 3 C 3 Ts c) NaN 3, DMF d) C 3 Cl K-tBu e) 3 P 4, heat f) NaCl 2

53 3. (9 pts) For each of the following pairs of molecules, identify any stereogenic centers, label them as having the (R) or the (S) configuration, and then indicate the relationship between the two molecules; are they enantiomers, diastereomers, or are they identical? (Klein Chapter 5) a) b) c) 4. (8 pts) Give all of the expected organic products from the following reaction and label those products as being major, minor, or very minor. Then give an explanation for your assignments. (Klein Chapter 8) 3

54 5. (12 pts) Give the major organic product formed under the following reaction conditions and then a detailed mechanism, using curved arrows to show bonds being formed and broken, to describe the transformation. (Klein Chapters 6-7) Draw a reaction profile on the axes below for the formation of the organic product above that includes structures of the reactant, any intermediate(s), and a transition state for the rate-determining step only. Potential energy Reaction coordinate 4

55 6. (8 pts) Which isomer undergoes faster E2 reaction with base, cis-1-bromo-4-t-butyl cyclohexane or trans-1- bromo-4-t-butylcyclohexane? Use diagrams to help with your explanation. (Klein Chapter 8) 7. (9 pts) Give each of the following molecules acceptable names; you may use trivial or IUPAC names for substituents as needed. (Klein Chapters 7-8) a) b) I Cl c) 5

56 8. (8 pts) Give a complete mechanism that accounts for the following conversion. The optical rotation (i.e. [α] D ) of the starting material is +54 ; what do you expect the rotation of the product to be, and why? (Klein Chapters 5-7) 8. (8 pts) In the boxes provided, give a structure of a suitable organic starting material that would be needed to produce the given product in each of the following cases. (Klein Chapters 7-8) a) Kt-Bu C 2 b) 2 S 4, heat c) NaN 3 in DMF N 3 d) 2 3 C 6

57 9. (18 pts) Answer each of the following questions by circling your choice and then giving a few words of explanation for why you made that choice. (Klein Chapters 7-8) a) Which of the following species is the better nucleophile? Why? b) Which of the following compounds would react faster in a solvolysis reaction with C 3? Why? c) Which of the following solvents would allow for faster S N 2 reactions? Why? d) Which of the following species is the better leaving group? Why? e) Which of the following compounds would completely deprotonate ethanol? Why? f) Which of the following compounds would react faster in S N 2 reactions? Why? 7

58 Chemistry 3719 Practice Exam B2 Key This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (8 pts) Provide a detailed mechanism, using curved arrows to show the breaking and forming of bonds, that accounts for the following conversion. (Klein Chapter 8) Alkyl migration to convert a secondary carbocation Into a more stable tertiary carbocation 1

59 2. (12 pts) Provide structures of the major and minor organic product(s) that are expected to be formed in each of the following situations. (Klein Chapters 7-8) a) NaC 3 + (Zaitsev) major minor b) C 3 C 3 3 C C3 (racemic, via 3 o carbocation) c) Ts N 3 NaN 3, DMF (inversion through S N 2) C 3 C 3 C 3 d) Cl K-tBu + (offman) major minor e) 3 P 4, heat + (Zaitsev) major minor f) NaCl Cl (via 2 o to 3 o carbocation rearrangment) 2

60 3. (9 pts) For each of the following pairs of molecules, identify any stereogenic centers, label them as having the (R) or the (S) configuration, and then indicate the relationship between the two molecules; are they enantiomers, diastereomers, or are they identical? (Klein Chapter 5) a) b) c) 4. (8 pts) Give all of the expected organic products from the following reaction and label those products as being major, minor, or very minor. Then give an explanation for your assignments. (Klein Chapter 8) 3

61 5. (12 pts) Give the major organic product formed under the following reaction conditions and then a detailed mechanism, using curved arrows to show bonds being formed and broken, to describe the transformation. (Klein Chapters 6-7) Draw a reaction profile on the axes below for the formation of the organic product above that includes structures of the reactant, any intermediate(s), and a transition state for the rate-determining step only. potential energy R.D.S. 2 Reaction coordinate 4

62 6. (8 pts) Which isomer undergoes faster E2 reaction with base, cis-1-bromo-4-t-butyl cyclohexane or trans-1- bromo-4-t-butylcyclohexane? Use diagrams to help with your explanation. (Klein Chapter 8) 7. (9 pts) Give each of the following molecules acceptable names; you may use trivial or IUPAC names for substituents as needed. (Klein Chapters 7-8) a) (E)-3-bromo-5-methylhept-2-ene b) (S)-5-iodo-3,3-dimethylcyclopent-1-ene I Cl c) 1-chloro-2-propylcyclohex-1-ene 5

63 8. (8 pts) Give a complete mechanism that accounts for the following conversion. The optical rotation (i.e. [α] D ) of the starting material is +54 ; what do you expect the rotation of the product to be, and why? (Klein Chapters 5-7) C 2 3 C C 3 2 C 3 C 3 = C 3 The chiral starting bromide converts to an achiral product so [α] D should be (8 pts) In the boxes provided, give a structure of a suitable organic starting material that would be needed to produce the given product in each of the following cases. (Klein Chapters 7-8) a) I Kt-Bu C 2 E2 b) 2 S 4, heat E1 c) NaN 3 in DMF N 3 S N 2 d) 3 C 2 3 C S N 1 6

64 9. (18 pts) Answer each of the following questions by circling your choice and then giving a few words of explanation for why you made that choice. (Klein Chapters 7-8) a) Which of the following species is the better nucleophile? Why? b) Which of the following compounds would react faster in a solvolysis reaction with C 3? Why? c) Which of the following solvents would allow for faster S N 2 reactions? Why? d) Which of the following species is the better leaving group? Why? e) Which of the following compounds would completely deprotonate ethanol? Why? f) Which of the following compounds would react faster in S N 2 reactions? Why? 7

65 Chemistry 3719 Practice Exam B3 This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (7 pts) Give a detailed mechanism that shows the main steps that lead to the two products in the following reaction. Include structures of any intermediates that are formed. (Klein Chapter 11) 1

66 2. (7 pts) Give the expected major product and then provide a detailed mechanism, using curved arrows to show the breaking and forming of bonds, for the following reaction. (Klein Chapter 10) 3. (7 pts) Give the expected major and minor products formed under the following conditions. Then give a mechanism for the formation of both the major and minor products. (Klein Chapter 11) 2

67 4. (18 pts) Provide structures of the major and minor organic product(s) that are expected to be formed in each of the following situations. When more than one reaction is involved, a product from each is required. (Klein Chapters 9-11) a) 2, heat b) C 3 dilute 2 S 4 c) 2, Pt C 3 d) Zn, 2 e) f) NaC 3 C 3 3

68 5. (8 pts) In the boxes provided, give a structure of the organic starting material that would be needed to provide the given product in each of the following cases. (Klein Chapters 10-11) a) 2, heat b) excess c) d) C 3 C 3 6. (9 pts) Give the major product formed from free radical bromination of the following molecules and then give a name for each of those products. (Klein Chapter 11) a) Methylcyclopentane b) 2,3-Dimethylbutane c) 2,2,4,4-Tetramethylpentane 4

69 7. (9 pts) Give each of the following compounds acceptable names. You may use either the IUPAC system or the common names for substituents. Watch out for any stereochemical issues (i.e cis/trans or R/S). (Klein Chapter 10) a. b. c. 8. (6 pts) In each of the series of molecules below, circle the most stabilized species, and then give a few words of explanation for your choice. (Klein Chapters 3-11) a) b) c) 5

70 9. (7 pts) Give all of the possible monobrominated products formed under the following conditions. Then provide a detailed mechanism, pushing curved arrows to describe all important bond-forming and bondbreaking events, that accounts for the formation of the major product in the following reaction. (Klein Chapter 11) 10. (7 pts) Provide a detailed mechanism for the following reaction that explains the bond-forming and bondbreaking steps on the way to the product. (Klein Chapter 9) 6

71 11. (7 pts) Provide a detailed mechanism, pushing curved arrows to describe bonds forming and breaking, that accounts for the formation of both products in the following reaction. (Klein Chapter 9) 12. (8 pts) Give the major and minor final products formed in each of the following situations, and then give an explanation for the different outcomes. (Klein Chapter 9) a) b) 7

72 Chemistry 3719 Practice Exam B3 Key This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (7 pts) Give a detailed mechanism that shows the main steps that lead to the two products in the following reaction. Include structures of any intermediates that are formed. (Klein Chapter 11) 1

73 2. (7 pts) Give the expected major product and then provide a detailed mechanism, using curved arrows to show the breaking and forming of bonds, for the following reaction. (Klein Chapter 10) 3. (7 pts) Give the expected major and minor products formed under the following conditions. Then give a mechanism for the formation of both the major and minor products. (Klein Chapter 11) 2

74 4. (18 pts) Provide structures of the major and minor organic product(s) that are expected to be formed in each of the following situations. When more than one reaction is involved, a product from each is required. (Klein Chapters 9-11) a) 2, heat (via 3 o radical) C 3 dilute 2 S 4 3 C b) (via 3 o carbocation) c) 2, Pt (via syn addition) d) C Zn, 2 C C 3 e) (via 3 o carbocation) f) NaC 3 C 3 (more highly substituted alkene formed - Zaitsev) 3

75 5. (8 pts) In the boxes provided, give a structure of the organic starting material that would be needed to provide the given product in each of the following cases. (Klein Chapters 10-11) a) 2, heat b) excess c) Na d) C 3 C 3 6. (9 pts) Give the major product formed from free radical bromination of the following molecules and then give a name for each of those products. (Klein Chapter 11) a) Methylcyclopentane b) 2,3-Dimethylbutane c) 2,2,4,4-Tetramethylpentane 4

76 7. (9 pts) Give each of the following compounds acceptable names. You may use either the IUPAC system or the common names for substituents. Watch out for any stereochemical issues (i.e cis/trans or R/S). (Klein Chapter 10) a. (R,Z)-hept-4-en-1-yn-3-ol b. (R)-3-bromo-3-ethynylcyclopent-1-ene c. Cl (R)-4-chlorohex-1-yne 8. (6 pts) In each of the series of molecules below, circle the most stabilized species, and then give a few words of explanation for your choice. (Klein Chapters 3-11) a) b) c) 5

77 9. (7 pts) Give all of the possible monobrominated products formed under the following conditions. Then provide a detailed mechanism, pushing curved arrows to describe all important bond-forming and bondbreaking events, that accounts for the formation of the major product in the following reaction. (Klein Chapter 11) 10. (7 pts) Provide a detailed mechanism for the following reaction that explains the bond-forming and bondbreaking steps on the way to the product. (Klein Chapter 9) 6

78 11. (7 pts) Provide a detailed mechanism, pushing curved arrows to describe bonds forming and breaking, that accounts for the formation of both products in the following reaction. (Klein Chapter 9) 12. (8 pts) Give the major and minor final products formed in each of the following situations, and then give an explanation for the different outcomes. (Klein Chapter 9) a) The outcome here is governed mainly by the relative steric interactions in the transition states of the hydroboration step. The large BR 2 group will avoid the more crowded end of the alkene; the oxidation step retains the regiochemistry and stereochemistry (syn addition) from the first step. b) In the acid-catalyzed addition of 2 to this unsymmetrical alkene the product distribution depends upon the type of carbocation that could be formed; the major product will be formed via the tertiary carbocation, which is more stabilized by hyperconjugation than the secondary (the Markovnikoff rule). 7

79 Chemistry 3719 Practice Exam C1 This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (6 pts) Label all of the sp 2 hybridized atoms within the following molecules. (Klein Chapter 1) a) b) NC 3 c) 1

80 2. (15 pts) Draw the required structures in each of the following situations. (Klein Chapter 4) a) The highest energy chair conformation of trans-1,2-dibromocyclohexane b) A Newman projection of a gauche conformation of n-octane along the C-2 C-3 bond axis. c) The less stable isomer of 1,2-diisopropylcyclopropane. d) A Newman projection of the most stable conformation of n-hexane along the C-3 C-4 bond axis e) A boat conformation of cyclohexane. 2

81 3. (15 pts) Give acceptable names for the following molecules. Trivial or IUPAC names may be used for substituents. (Klein Chapter 4) a) b) c) d) C(C 3 ) 3 C(C 3 ) 2 e) 3

82 4. (15 pts) Give the products from each of the following acid-base reactions. Then give the acids on each side of the equations approximate pka values and indicate in each case if you expect the reaction to be exothermic, endothermic, or approximately thermoneutral in each case. (Klein Chapter 3) a) Li + 2 b) Li + c) C 3 C C + LiN(C 3 ) 2 d) C 3 C 2 NLi + N e) + C 3 C 2 C 2 K 4

83 5. (9 pts) Draw acceptable structures for each of the following molecules. (Klein Chapter 4) a) trans-1-ethyl-3-isopropylcyclopentane b) Cyclopentylcyclohexane c) 2,4,4-Trimethyl-3-octanol 6. (10 pts) Draw all of the isomers possible for C 6 14 and then give each structure an acceptable name. (Klein Chapter 4) 5

84 7. (8 pts) For the highlighted atom in the following molecules, fill in the ground state electronic configuration on the left, and then draw a picture on the right of the hybridization model that best explains the bonding of the highlighted atoms. (Klein Chapter 1) 8. (6 pts) Which of the two molecules below is the stronger acid? Give their approximate pka values and explain your choice in terms of the structures and relative stabilities of the respective conjugate bases. (Klein Chapter 3) 6

85 9. (6 pts) Draw a second resonance structure for the following anions and then an overall resonance hybrid for each. (Klein Chapter 2) 10. (10 pts) Consider the cis- and trans- isomers 1-t-butyl-3-ethylcyclohexane. (Klein Chapter 4) a. Draw the lowest energy ring conformation for both isomers and explain your choices. b. Indicate which isomer is less stable and explain your reasoning using a diagram to highlight any destabilizing interactions. 7

86 Chemistry 3719 Practice Exam C1 Key This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (6 pts) Label all of the sp 2 hybridized atoms within the following molecules. (Klein Chapter 1) a) b) NC 3 c) 1

87 2. (15 pts) Draw the required structures in each of the following situations. (Klein Chapter 4) a) The highest energy chair conformation of trans-1,2-dibromocyclohexane b) A Newman projection of a gauche conformation of n-octane along the C-2 C-3 bond axis. c) The less stable isomer of 1,2-diisopropylcyclopropane. d) A Newman projection of the most stable conformation of n-hexane along the C-3 C-4 bond axis C 2 C 3 C 2 C 3 e) A boat conformation of cyclohexane. 2

88 3. (15 pts) Give acceptable names for the following molecules. Trivial or IUPAC names may be used for substituents. (Klein Chapter 4) a) 6-ethyl-3,5,5-trimethylnonane b) bicyclo[5.3.0]decane c) 6-isopropyl-2,5-dimethylundecane C(C 3 ) 2 d) trans-1-(tert-butyl)-3-isopropylcyclohexane C(C 3 ) 3 e) 6-cyclopropyl-2,3-dimethylheptane 3

89 4. (15 pts) Give the products from each of the following acid-base reactions. Then give the acids on each side of the equations approximate pka values and indicate in each case if you expect the reaction to be exothermic, endothermic, or approximately thermoneutral in each case. (Klein Chapter 3) a) Li + 2 exothermic + Li base acid: pka ~ 16 pka ~ 50 b) Li + thermoneutral + Li base acid: pka ~ 16 pka ~ 16 c) C 3 C C + LiN(C 3 ) 2 exothermic C 3 C CLi + N(C 3 ) 2 acid: pka ~ 25 base pka ~ 38 d) C 3 C 2 NLi + N thermoneutral C 3 C 2 N 2 base acid: pka ~ 38 pka ~ 38 + N Li e) + C 3 C 2 C 2 K exothermic K + C 3 C 2 C 2 acid: pka ~ 10 base acid: pka ~ 16 4

90 5. (9 pts) Draw acceptable structures for each of the following molecules. (Klein Chapter 4) a) trans-1-ethyl-3-isopropylcyclopentane b) Cyclopentylcyclohexane c) 2,4,4-Trimethyl-3-octanol 6. (10 pts) Draw all of the isomers possible for C 6 14 and then give each structure an acceptable name. (Klein Chapter 4) 5

91 7. (8 pts) For the highlighted atom in the following molecules, fill in the ground state electronic configuration on the left, and then draw a picture on the right of the hybridization model that best explains the bonding of the highlighted atoms. (Klein Chapter 1) 8. (6 pts) Which of the two molecules below is the stronger acid? Give their approximate pka values and explain your choice in terms of the structures and relative stabilities of the respective conjugate bases. (Klein Chapter 3) The electron-withdrawing C= in the carboxylic acid makes the proton more positive than in the alcohol, and the C= also allows the charge in the anion to delocalize thus making the conjugate base more stable. 6

92 9. (6 pts) Draw a second resonance structure for the following anions and then an overall resonance hybrid for each. (Klein Chapter 2) 10. (10 pts) Consider the cis- and trans- isomers 1-t-butyl-3-ethylcyclohexane. (Klein Chapter 4) a. Draw the lowest energy ring conformation for both isomers and explain your choices. This conformation of the cis isomer can have both substituents equatorial thus avoiding any destabilizing 1,3-diaxial interactions that would occur in the ring-flipped conformation. The trans isomer has to have one substituent axial and will prefer the conformation in which the smaller ethyl group is axial and not the larger t-butyl group, which would inevitably have significantly more destabilizing 1,3-interactions. b. Indicate which isomer is less stable and explain your reasoning using a diagram to highlight any destabilizing interactions. The trans isomer is less stable here since in either ring conformation one of the bulky groups will have to be in an axial position thus destabilizing the system due to 1,3-diaxial interactions (below). 7

93 Chemistry 3719 Practice Exam C2 This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1) (10 pts) Give a complete mechanism for how both products are formed in the following reaction. Which product do you expect to be major and which minor? iefly explain your answer. (Klein Chapter 8) 1

94 2) (18 pts) Give organic product(s), labeling major and minor where applicable, for the following reactions. (Klein Chapters 7-8) a) 3 C 2 S 4, b) KCN, DMF c) C 3 Cl d) Cl NaC 3 C 3, e) f) 3 C S 2 CF 3 Kt-Bu 2

95 3) (10 pts) Give the major organic product expected below, then a draw the reaction profile (potential energy vs. reaction coordinate) for the conversion that includes pictures of the transition state(s) involved. (Klein Chapters 6-7) Potential energy Reaction coordinate 4) (9 pts) Give acceptable names for each of the following molecules. (Klein Chapters 5-8) a) b) Cl c) 3

96 5) (8 pts) Give the major organic products formed under the following conditions and a detailed mechanism that explains their formation. Will the product mixture have an optical rotation or will [α] D = 0? (Klein Chapter 7) 6) (9 pts) Give structures for each of the following molecules. (Klein Chapters 7-8) a) (E)-4-Methyl-3-hexen-2-ol b) 1-omo-5-tert-butylcyclohex-1-ene c) trans-2-isopropenylcyclopentanol 4

97 7) (12 pts) Tamiflu has been developed by Roche Pharmaceuticals to alleviate the symptoms caused by the influenza virus. The 14-step synthesis of Tamiflu begins with the chiral natural product shikimic acid (below). Identify all of the stereocenters in both shikimic acid and Tamiflu and label them as having the (R) or (S) configuration. (Klein Chapter 5) shikimic acid 14 steps Roche Pharmaceuticals N 2 N Tamiflu 8) (8 pts) Working out the configurations of the chiral centers (i.e. R or S) will help in the following questions. (Klein Chapter 5) a. Convert the following wedge-dash depiction into a Fischer projection. b. What is the relationship between the following molecules (same, enantiomers, diastereomers)? 5

98 9) (10 pts) Provide explanations, using Newman projections, to explain the following product outcomes. (Klein Chapter 8) a) b) 10) (6 pts) In each of the following cases, circle your choice and then give a few words of explanation for why you made that choice. (Klein Chapter 7) a. Reacts faster in S N 2 reactions with NaN 3 as the nucleophile? b. Better solvent in S N 1 reactions? c. Better nucleophile in S N 2 reactions? 6

99 Chemistry 3719 Practice Exam C2 Key This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1) (10 pts) Give a complete mechanism for how both products are formed in the following reaction. Which product do you expect to be major and which minor? iefly explain your answer. (Klein Chapter 8) 2 S 4 heat Rearrangement occurs where the more stable tetrasubstituted alkene is preferred over trisubstituted alternative; sp 2 hybrid C in alkenes is stabilized by alkyl groups through induction, thus the more alkyl groups the better the alkene. 1

100 2) (18 pts) Give organic product(s), labeling major and minor where applicable, for the following reactions. (Klein Chapters 7-8) a) 3 C 2 S 4, 3 C + 3 C E1 - Zaitsev major minor b) KCN, DMF CN only inverted product via S N 2 c) C 3 Cl Cl C 3 + C 3 Cl racemic mixture via S N 1 Cl d) NaC 3 C 3, + E2 - Zaitsev major minor e) only product via S N 2 f) 3 C S 2 CF 3 Kt-Bu E2 - ofmann 3 C major + 3 C minor 2

101 3) (10 pts) Give the major organic product expected below, then a draw the reaction profile (potential energy vs. reaction coordinate) for the conversion that includes pictures of the transition state(s) involved. (Klein Chapters 6-7) Cl S N 2 Cl (+ 2 ) Potential energy + - Cl Cl Cl 2 Cl Reaction coordinate 4) (9 pts) Give acceptable names for each of the following molecules. (Klein Chapters 5-8) a) b) c) 3

102 5) (8 pts) Give the major organic products formed under the following conditions and a detailed mechanism that explains their formation. Will the product mixture have an optical rotation or will [α] D = 0? (Klein Chapter 7) In this S N 1 reaction the leaving group breaks away to leave a flat carbocation that has three different alkyl groups attached. When the bromide nucleophile attacks it may do so from either face of the cation to produce enantiomeric products in approximately equal amounts. The optical rotation of this racemic mixture will therefore be zero as the rotations of the enantiomers will cancel. 6) (9 pts) Give structures for each of the following molecules. (Klein Chapters 7-8) a) (E)-4-Methyl-3-hexen-2-ol b) 1-omo-5-tert-butylcyclohex-1-ene c) trans-2-isopropenylcyclopentanol 4

103 7) (12 pts) Tamiflu has been developed by Roche Pharmaceuticals to alleviate the symptoms caused by the influenza virus. The 14-step synthesis of Tamiflu begins with the chiral natural product shikimic acid (below). Identify all of the stereocenters in both shikimic acid and Tamiflu and label them as having the (R) or (S) configuration. (Klein Chapter 5) (S) (R) (R) shikimic acid 14 steps Roche Pharmaceuticals N (R) 2 N (S) (R) Tamiflu 8) (8 pts) Working out the configurations of the chiral centers (i.e. R or S) will help in the following questions. (Klein Chapter 5) a. Convert the following wedge-dash depiction into a Fischer projection. b. What is the relationship between the following molecules (same, enantiomers, diastereomers)? 5

104 9) (10 pts) Provide explanations, using Newman projections, to explain the following product outcomes. (Klein Chapter 8) a) b) 10) (6 pts) In each of the following cases, circle your choice and then give a few words of explanation for why you made that choice. (Klein Chapter 7) F07 Exam 3 a. Reacts faster in S N 2 reactions with NaN 3 as the nucleophile? b. Better solvent in S N 1 reactions? c. Better nucleophile in S N 2 reactions? 6

105 Chemistry 3719 Practice Exam C3 This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (9 pts) Give the major and minor alkyl halide products expected from the following reaction and then show a mechanism (using curved arrows) that describes how the major product is formed during the reaction. (Klein Chapter 11) 1

106 2. (18 pts) Give the expected major products from each of the following reactions. When more than one set of reagents are given the major product from each step is required. Where stereochemistry is an issue, label the products as being either single stereoisomers, enantiomers, or diastereomers. (Klein Chapters 7-10) a Zn, 2 b. Cl NaCN DMS,50 o C c. 1.-B(C 6 11 ) 2 2.Na, 2 2 d. 2 e. C 3 C 3 f. C C 1.NaN 2 2.C 3 C 2 I 2

107 3. (8 pts) Give the major and minor product(s) from the following reaction and then a complete mechanism (using curved arrows) for the formation of the major product. Explain briefly why this product is major. (Klein Chapter 9) 4. (12 pts) Draw acceptable structures for each of the following molecules. (Klein Chapters 7-10) a. (4S,5S)-5,7-dimethyl-1-octyn-4-ol b. (2R,3S,Z)-2-bromo-5-fluoro-3-methyl-4-heptene c. (1R,2S)-1-bromo-2-isopropylcyclohexane 3

108 5. (12 pts) Provide the major product from each step of the following reaction sequence: (Klein Chapter 10) 6. (8 pts) Give an explanation for the different product outcomes in the following reactions. (Klein Chapter 11) 4

109 7. (8 pts) Draw the organic product produced under the following ozonolysis conditions; then draw a detailed mechanism for its formation. (Klein Chapter 9) 8. (8 pts) In each of the following reactions give a mechanistic explanation that accounts for the observed regiochemistry and/or stereochemistry in each product. (Klein Chapter 9) a. Explain the observed stereochemistry and regiochemistry in the following hydroboration: b. Explain the observed stereochemistry in the following addition of 2 : 5

110 9. (9 pts) Provide a complete mechanism for the following conversion. (Klein Chapter 9) 10. (8 pts) Give the expected product from the following portion of the hydroboration-oxidation sequence and a mechanism for its formation. Be careful to account for any important stereochemical issues. (Klein Chapter 9) 6

111 Chemistry 3719 Practice Exam C3 Key This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (9 pts) Give the major and minor alkyl halide products expected from the following reaction and then show a mechanism (using curved arrows) that describes how the major product is formed during the reaction. (Klein Chapter 11) 1

112 2. (18 pts) Give the expected major products from each of the following reactions. When more than one set of reagents are given the major product from each step is required. Where stereochemistry is an issue, label the products as being either single stereoisomers, enantiomers, or diastereomers. (Klein Chapters 7-10) a Zn, b. Cl NaCN DMS, 50 o C CN S N 2 reaction only gives the one (inverted) product c. 1. -B(C 6 11 ) 2 1. B(C 6 11 ) Na, 2 2 d. 2 + (R,R) (S,S) Enantiomers formed (50/50) e. C 3 C 3 + Diastereomers formed (~50/50) f. C C 1. NaN 2 2. C 3 C 2 I 1. C C 2. C CC 2C 3 2

113 3. (8 pts) Give the major and minor product(s) from the following reaction and then a complete mechanism (using curved arrows) for the formation of both products. Explain briefly why one product is major. (Klein Chapter 9) The major product in this electrophilic addition reaction is produced via the more stabilized tertiary carbocation, which is preferred over the alternative secondary carbocation, due to increased hyperconjugation; the tertiary carbocation has more adjacent (beta) σ bonds, which are able to share electron density with the electron-poor positive carbon. 4. (12 pts) Draw acceptable structures for each of the following molecules. (Klein Chapters 7-10) a. (4S,5S)-5,7-dimethyl-1-octyn-4-ol b. (2R,3S,Z)-2-bromo-5-fluoro-3-methyl-4-heptene c. (1R,2S)-1-bromo-2-isopropylcyclohexane 3

114 5. (12 pts) Provide the major product from each step of the following reaction sequence: (Klein Chapter 10) 1. 2 in CCl 4 2. excess NaN 2 then + quench 3. C 3 C 2 C 2 C 2 Li 4. C 3 C 2 C 2 5. Na, liq. N 3 6. C 3 C Na (8 pts) Give an explanation for the different product outcomes in the following reactions. (Klein Chapter 11) The difference in the product distributions is due to the difference in the stability of the and the Cl radicals. The radical is more stable and is therefore able to be more selective when it comes to abstracting a hydrogen atom to produce a carbon radical. In this case the more stabilized 2 o radical is formed preferably leading to the 2 o alkyl halide being the vast majority of the product. The Cl radical is much more reactive, and therefore less selective, resulting in significantly more of the 1 o alkyl halide product being formed with Cl 2 as the halogen radical source. 4

115 7. (8 pts) Draw the organic product produced under the following ozonolysis conditions; then draw a detailed mechanism for its formation. (Klein Chapter 9) 8. (8 pts) In each of the following reactions give a mechanistic explanation that accounts for the observed regiochemistry and/or stereochemistry in each product. (Klein Chapter 9) a. Explain the observed stereochemistry and regiochemistry in the following hydroboration: This reaction involves a syn addition of the B 3 molecule hence the shown cis stereochemical outcome. The regiochemical preference is explained by the smaller bonding to the less accessible carbon of the alkene and the larger B 2 group adding to the less hindered carbon. b. Explain the observed stereochemistry in the following addition of 2 : This addition reaction involves the formation of a carbocation that is stabilized by donation of electron density from the first that has added (bromonium ion). The large then blocks one face of the molecule such that the bromide ion may only attack from the opposite face, hence the trans stereochemistry. 5

116 9. (9 pts) Provide a complete mechanism for the following conversion. 10. (8 pts) Give the expected product from the following portion of the hydroboration-oxidation sequence and a mechanism for its formation. Be careful to account for any important stereochemical issues. (Klein Chapter 9) The migration step is concerted and the initial stereochemistry of the addition (syn) is retained to give the product shown. 6

117 Chemistry 3719, Fall 2013 Exam 1 Student Name: Y Number: This exam is worth 100 points out of a total of 700 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam. Good Luck! 1. (8 pts) For the highlighted atom in the following molecules, fill in the ground state electronic configuration from the periodic table on the left, and then draw a picture on the right of the hybridization model that best explains the atomic orbitals used in bonding by the highlighted atoms. Energy hybridize C N Energy hybridize 1

118 2. (10 pts) Provide the required values for each of the following species as indicated. a. Give each of the following atoms an approximate electronegativity value: b. Give each of the following acids an approximate pka value: 3. (9 pts) In each of the following pairs of molecules one of the two is more stable than the other. Circle the more stable molecule and then briefly explain your choices in the space on the right. a. Li vs. Li b. C 2 vs. c. F F F Li vs. Li 2

119 4. (9 pts) Provide each of the following alkane derivatives with an acceptable name. You may use either the common or IUPAC names for substituents. a. b. c. 5. (9 pts) For the following systems, draw all of the other important resonance structures, including any lone pairs, and then a resonance hybrid for each molecule. a. b. c. 3

120 6. (12 pts) Give the products expected from each of the following acid-base reactions. Then label each acid with an approximate pk a and indicate whether deprotonation will be complete or incomplete in each case. a. + KC 2 C 3 b. + Na c. NLi + 7. (8 pts) The following molecule has been designed as a synthetic intermediate in the formation of glutathione drug analogs. Identify each of the eight (8) functional groups contained within the molecule. 4

121 8. (9 pts) In each of the pairs of compounds below, indicate whether the structures are related as stereoisomers, constitutional isomers, or are the same compound. Then circle the more stable of the two structures and give a few words of explanation for your choices. a. C 3 and 3 C C 3 C 3 b. 3 C C 3 and 3 C C 3 c. and 9. (8 pts) For each of the following structures, add any missing lone pairs that are needed and label any formal charges that are necessary. a. b. N c. d. 5

122 10. (9 pts) Draw Newman depictions that correspond to the following conformations. a. The most stable conformation of 2-methyloctane along the C-4 C-5 bond. b. The least stable conformation of 2,2-dimethylhexane along the C-3 C-4 bond. c. A gauche conformation for hexylcyclopropane along the C-3 C-4 bond of the hexyl chain. 11. (9 pts) For each of the three molecules below, indicate whether you expect them to be a solid, liquid, or gas at room temperature and whether you expect them to dissolve in water or not. Explain your choices briefly. anthracene sucrose 1-octanol 6

123 Chemistry 3719, Fall 2013 Exam 1 Key Student Name: Y Number: This exam is worth 100 points out of a total of 700 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam. Good Luck! 1. (8 pts) For the highlighted atom in the following molecules, fill in the ground state electronic configuration from the periodic table on the left, and then draw a picture on the right of the hybridization model that best explains the atomic orbitals used in bonding by the highlighted atoms. lone pairs to bonds Energy hybridize sp 3 to bonds lone pair to bond C N Energy hybridize sp p 1

124 2. (10 pts) Provide the required values for each of the following species as indicated. a. Give each of the following atoms an approximate electronegativity value: b. Give each of the following acids an approximate pka value: 3. (9 pts) In each of the following pairs of molecules one of the two is more stable than the other. Circle the more stable molecule and then briefly explain your choices in the space on the right. a. Li vs. Li A negative charge on a highly electronegative atom such as is more stable than on C b. C 2 vs. The lone pair on the right will delocalize such that some of the charge will be on and not C c. F F F Li vs. Li The highly electronegative F atoms will help to spread negative charge through induction 2

125 4. (9 pts) Provide each of the following alkane derivatives with an acceptable name. You may use either the common or IUPAC names for substituents. a. bicyclo[3.3.3]undecane b. 2-isobutyl-5-isopropyl-1,1-dimethylcycloheptane c. 3,5-diethyl-6,7,7-trimethyldecane 5. (9 pts) For the following systems, draw all of the other important resonance structures, including any lone pairs, and then a resonance hybrid for each molecule. a b c

126 6. (12 pts) Give the products expected from each of the following acid-base reactions. Then label each acid with an approximate pk a and indicate whether deprotonation will be complete or incomplete in each case. K a. + KC 2 C 3 + C 2 C 3 K ~10 6 complete pka =10 deprotonation pka =16 b. Na + Na + K ~1 incomplete pka =16 deprotonation pka =16 Li c. NLi + N K ~10 13 complete pka =25 deprotonation pka = (8 pts) The following molecule has been designed as a synthetic intermediate in the formation of glutathione drug analogs. Identify each of the eight (8) functional groups contained within the molecule. 4

127 8. (9 pts) In each of the pairs of compounds below, indicate whether the structures are related as stereoisomers, constitutional isomers, or are the same compound. Then circle the more stable of the two structures and give a few words of explanation for your choices. a. C 3 C 3 and 3 C C 3 Same compound; right-hand is more stable since both groups are equatorial thus avoiding 1,3- diaxial interactions b. 3 C C 3 and 3 C C 3 Stereoisomers; having both C 3 groups on opposite sides of the molecule reduces steric strain c. and Constitutional isomers; right-hand is more stable since it will have less ring strain (no cyclopropane) 9. (8 pts) For each of the following structures, add any missing lone pairs that are needed and label any formal charges that are necessary. a. b. N c. d. 5

128 10. (9 pts) Draw Newman depictions that correspond to the following conformations. a. The most stable conformation of 2-methyloctane along the C-4 C-5 bond. b. The least stable conformation of 2,2-dimethylhexane along the C-3 C-4 bond. c. A gauche conformation for hexylcyclopropane along the C-3 C-4 bond of the hexyl chain. 11. (9 pts) For each of the three molecules below, indicate whether you expect them to be a solid, liquid, or gas at room temperature and whether you expect them to dissolve in water or not. Explain your choices briefly. anthracene sucrose 1-octanol Anthracene is a solid since it has the formula C and there will be significant intermolecular dispersion forces holding molecules to each other. This compound is very non-polar so it would not be expected to be soluble in water. Sucrose has many groups which will allow -bonding between molecules and cause this to be a solid. The groups also make the compound polar and, combined with the -bonding, will make this material very soluble in water. 1-ctanol is a liquid since the greasy chain will only allow for weak intermolecular forces but the group will give some -bonding. The non-polar alkyl chain will outweigh the group so this alcohol would not be expected to be soluble in water. 6

129 Chemistry 3719, Fall 2013 Exam 2 Student Name: Y Number: This exam is worth 100 points out of a total of 700 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam. Good Luck! 1. (10 pts) Draw two chair conformations for cis-1-t-butyl-4-ethylcyclohexane that are related through a ringflip. Then circle which conformation you expect to be more stable and explain why. Then do the same for the trans isomer and, finally, indicate whether the cis or trans isomer should be more stable overall and explain your choice. 1

130 2. (15 pts) Give the expected products, major and minor where applicable, in each of the following situations. Be sure to take into account any changes in stereochemistry that may occur. If more than one set of reagents is employed, product(s) from each step is/are required. a. C 3 NaCN, DMS b. KC(C 3 ) 3 c. 3 C 1. S 2 Cl pyridine 2. NaS, DMS d. C 3 I C 3 e. NaN 2,DMS 2

131 3. (9 pts) Provide each of the following molecules with an acceptable name. You may use either the common or IUPAC names for substituents and be careful to include any stereochemical descriptors where needed. a. Cl b. F C 3 C 2 C 3 c. F 4. (10 pts) n the axes given below, draw a complete reaction profile for the following reaction that includes diagrams of all intermediates and transition states involved. 3

132 5. (9 pts) In the boxes provided, identify the type of arrow-pushing process in each step within the following reaction mechanisms (i.e. nucleophilic attack, leaving group leaving, proton transfer, or rearrangement). a. b c (9 pts) The following solvolysis conditions give two major products in equal amounts and, when measured for the mixture, [ ] D = 0. Provide the products and a mechanism for this process, as well as an explanation for the optical rotation data. Cl 2 4

133 7. (9 pts) For each of the following pairs of molecules, provide the configuration of any chiral centers and then indicate whether the two molecules within each pair are enantiomers, diastereomers, or are identical. a. and b. C 3 Cl C 3 and 3 C Cl C 3 c. and 8. (9 pts) The following substitution reaction begins with an enantiomerically pure starting material (i.e. only the R isomer) which has [ ] D = +53 and, after the reaction, the isolated product has [ ] D = -35. Explain how this data helps you to decide which mechanism (S N 1 or S N 2) is operating here and suggest a simple experiment that would back up your choice. Push arrows to show the mechanism and give a product. :P(C 2 C 2 C 2 C 3 ) 3 ether 5

134 9. (10 pts) The molecule below is aterumalide ND, a potent anti-tumor drug. Identify 5 (five) chiral centers within the compound and label them as being either the R or S configuration. Cl Ac C 3 C 2 C (10 pts) Provide a detailed mechanism for the following transformation that uses curved arrows to show the breaking and forming of bonds. Identify each type of arrow-pushing process that you use and explain why this bromide is the major product formed. 6

135 Chemistry 3719, Fall 2013 Exam 2 - Key Student Name: Y Number: This exam is worth 100 points out of a total of 700 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam. Good Luck! 1 1. (10 pts) Draw two chair conformations for cis-1-t-butyl-4-ethylcyclohexane that are related through a ringflip. Then circle which conformation you expect to be more stable and explain why. Then do the same for the trans isomer and, finally, indicate whether the cis or trans isomer should be more stable overall and explain your choice. 1

136 2. (15 pts) Give the expected products, major and minor where applicable, in each of the following situations. Be sure to take into account any changes in stereochemistry that may occur. If more than one set of reagents is employed, product(s) from each step is/are required. a. C 3 NaCN, DMS C 3 CN S N 2 with inversion b. KC(C 3 ) 3 + major (large base is used) c. 3 C 1. S 2 Cl pyridine 1. Ts 2. S 2. NaS, DMS S N 2 with inversion d. C 3 I C 3 C 3 C 3 C 3 C 3 + S N 1 - Racemix mixture formed (~50:50) e. NaN 2,DMS Intramolecular S N 2 2

137 3. (9 pts) Provide each of the following molecules with an acceptable name. You may use either the common or IUPAC names for substituents and be careful to include any stereochemical descriptors where needed. Cl a. (2S,5S)-2-chloro-5-ethyloctane C 3 b. F (2S,3S)-2-bromo-3-fluoropentane C 2 C 3 c. (R,E)-5-fluoro-6-methylhept-3-ene F 4. (10 pts) n the axes given below, draw a complete reaction profile for the following reaction that includes diagrams of all intermediates and transition states involved. 3

138 5. (9 pts) In the boxes provided, identify the type of arrow-pushing process in each step within the following reaction mechanisms (i.e. nucleophilic attack, leaving group leaving, proton transfer, or rearrangement). a. proton transfer rearrangement Nu: attack b proton transfer L.G. leaves proton transfer c L.G. leaves Nu: attack proton transfer 6. (9 pts) The following solvolysis conditions give two major products in equal amounts and, when measured for the mixture, [α]d = 0. Provide the products and a mechanism for this process, as well as an explanation for the optical rotation data. Cl 2 S N 1! + enantiomers formed in equal amounts so optical rotations cancel and [ ] D = 0 Leaving group leaves 2 Proton transfer Nu: attacks flat carbocation that is attacked equally from both sides 4

139 7. (9 pts) For each of the following pairs of molecules, provide the configuration of any chiral centers and then indicate whether the two molecules within each pair are enantiomers, diastereomers, or are identical. a. (S) (S) and (S) (R) diastereomers b. C 3 Cl C 3 and Cl 3 C (R) (R) C 3 enantiomers (S, S) c. and identical 8. (9 pts) The following substitution reaction begins with an enantiomerically pure starting material (i.e. only the R isomer) which has [α]d = +53 and, after the reaction, the isolated product has [α]d = -35. Explain how this data helps you to decide which mechanism (SN1 or SN2) is operating here and suggest a simple experiment that would back up your choice. Push arrows to show the mechanism and give a product. The fact that the chiral starting material produces a chiral product is only reconcilable with the S N2 mechanism; the S N1 mechanism would produce a racemic mixture of products for which [α] D = 0 because the rotations of the equal amounts of the R and S enantiomers would cancel. A simple experiment to support the S N2 assignment would be to add more nucleophile; the reaction would go faster if this is actually a second order reaction in which the nucleophile is involved in achieving the transition state in the rate-determining step. 5

140 9. (10 pts) The molecule below is aterumalide ND a potent anti-tumor drug. Identify 5 chiral centers within the compound and label them as being either the R or S configuration. 10. (10 pts) Provide a detailed mechanism for the following transformation that uses curved arrows to show the breaking and forming of bonds. Identify each type of arrow-pushing process that you use and explain why this bromide is the major product formed. Protonation by produces an excellent leaving group which breaks away to leave a secondary carbocation; this then undergoes alkyl rearrangement, with expansion of the strained cyclobutyl ring, to produce a more stable cyclopentyl tertiary carbocation which is finally trapped by the nucleophile to give the tertiary bromide. 6

141 Chemistry 3719, Fall 2013 Exam 3 Student Name: Y Number: This exam is worth 100 points out of a total of 700 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam. Good Luck! 1. (10 pts) Provide a detailed mechanism for the formation of the major product in the following conversion, using curved arrows to describe the making and breaking of bonds, and then explain the regiochemical and stereochemical outcomes in terms of the reactive intermediate(s) involved. 1

142 2. (15 pts) Give the expected major products in each of the following situations. Be sure to take into account any changes in stereochemistry that may occur. If more than one set of reagents is employed, product(s) from each step is/are required. a. 1. excess NaN b. 1. NaN 2,TF 2. C 3 C 2 C 2 c. 1. B 2. Na, 2 2 d. C 3 C 3 1. C 3 C / 2 e. C , heat 2. Kt-Bu, TF 2

143 3. (9 pts) Provide each of the following molecules with an acceptable name. You may use either the common or IUPAC names for substituents and be careful to include any stereochemical descriptors where needed. a. F b. c. 4. (10 pts) n the axes given below, draw a complete reaction profile for the following addition reaction that includes diagrams of all intermediates and transition states involved. Then indicate which step is ratedetermining and whether that step is unimolecular or bimolecular. 3

144 5. (9 pts) Provide a complete mechanism for the following conversion that features curved arrows to describe the making and breaking of bonds. Why is a ketone formed and not an aldehyde in this reaction? 6. (9 pts) The following conditions induce a free radical halogenation process at the allylic position with only two alkyl halide products being formed with a combined [ ] D = 0. Give a complete mechanism for the formation of the alkyl bromide products and an explanation for the optical rotation data. 4

145 7. (9 pts) For each of the following pairs of structures, circle the one that should be more stable. Then write a few words of explanation for your choices. a. C 2 C 2 and b. and Ac Ac c. g and g 8. (9 pts) Give a detailed mechanism for the following ozonolysis reaction that uses curved arrows to show the making and breaking of all bonds. What is the driving force (i.e. thermodynamic motivation) for this kind of process that results in both carbon-carbon sigma and pi bonds being broken? 5

146 9. (12 pts) Provide a sequence of reagents and conditions that would allow for the following conversions. Show the expected major products from each step of your syntheses. 3 C? 3 C 3 C 3 C C 3? 10. (8 pts) Explain why the following reactions give such different outcomes in terms of the percentages of products formed. Discuss the radicals formed and the transition states for -abstraction in each case. Cl 2, h 2, h + Cl 72% 28% % 0% Cl 6

147 Chemistry 3719, Fall 2013 Exam 3 - Key Student Name: Y Number: This exam is worth 100 points out of a total of 700 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam. Good Luck! 1. (10 pts) Provide a detailed mechanism for the formation of the major product in the following conversion, using curved arrows to describe the making and breaking of bonds, and then explain the regiochemical and stereochemical outcomes in terms of the reactive intermediate(s) involved. The regiochemical outcome is a consequence of a bromine radical abstracting on a tertiary carbon to produce a tertiary radical (stabilized by hyperconjugation). The stereochemical outcome is the consequence of adding a radical to either face of a planar (prochiral) alkene, which produces a planar (prochiral) radical that then abstracts from. verall two new stereocentres and 4 stereoisomers are formed. 1

148 2. (15 pts) Give the expected major products in each of the following situations. Be sure to take into account any changes in stereochemistry that may occur. If more than one set of reagents is employed, product(s) from each step is/are required. a. 1. excess NaN b. 1. NaN 2, TF 2. C 3 C 2 C c. 1. B 1. B Na, 2 2 (+/-) (+/-) d. C 3 C 3 1. C 3 C / 2 1. C 3 C 3 meso 2. C 3 C 3 (+/-) e. C , heat 2. Kt-Bu, TF 1. C 3 2. C 2 or C 3 (+/-) 2

149 3. (9 pts) Provide each of the following molecules with an acceptable name. You may use either the common or IUPAC names for substituents and be careful to include any stereochemical descriptors where needed. a. F (R)-5-fluorohex-1-yne b. (Z)-cyclooct-1-en-3-yne c. (1R,2S)-1-ethynyl-2-vinylcyclohexane 4. (10 pts) n the axes given below, draw a complete reaction profile for the following addition reaction that includes diagrams of all intermediates and transition states involved. Then indicate which step is ratedetermining and whether that step is unimolecular or bimolecular. 3

150 5. (9 pts) Provide a complete mechanism for the following conversion that features curved arrows to describe the making and breaking of bonds. Why is a ketone formed and not an aldehyde in this reaction? A ketone is formed because the first addition of + to the alkyne will form a secondary-like carbocation instead of a less stable primary-like carbocation. 6. (9 pts) The following conditions induce a free radical halogenation process at the allylic position with only two alkyl halide products being formed with a combined [α]d = 0. Give a complete mechanism for the formation of the alkyl bromide products and an explanation for the optical rotation data. During the first -abstraction step a planar allylic radical is formed which then reacts with either 2 or radical from either face to produce a racemic mixture of enantiomeric products. Due to the symmetry within the molecule reaction at either C-1 or C-3 of the allylic radical will give the same products regardless of where reaction takes place. 4

151 7. (9 pts) For each of the following pairs of structures, circle the one that should be more stable. Then write a few words of explanation for your choices. a. C 2 C 2 and Benzylic radical will be stabilized by resonance delocalization b. and Trisubstituted alkene features three electron-donating alkyl groups that help stabilize sp 2 carbon atoms Ac Ac c. g and g Mercurinium ion has all atoms with full complement of electrons; the carbocation has a 6-electron C atom 8. (9 pts) Give a detailed mechanism for the following ozonolysis reaction that uses curved arrows to show the making and breaking of all bonds. What is the driving force (i.e. thermodynamic motivation) for this kind of process that results in both carbon-carbon sigma and pi bonds being broken? zone is a very reactive molecule that features weak - bonds that get the chance to break during the ozonolysis process. In the first step the weaker - and C-C pi bonds are swapped for sigma bonds to form the molozonide, and in the second step one of the weak - bonds is broken, along with the C-C sigma bond. The resultant recombination produces the ozonide shown above. 5

152 9. (12 pts) Provide a sequence of reagents and conditions that would allow for the following conversions. Show the expected major products from each step of your syntheses. 3 C 3 C? 3 C 3 C C 3 NaN 2 excess 2, Pt 3 C 3 C C 3 3 C 3 C C 3? 2, RT 3 + quench xs. NaN (8 pts) Explain why the following reactions give such different outcomes in terms of the percentages of products formed. Discuss the radicals formed and the transition states for -abstraction in each case. In both reactions there is competition between the formation of tertiary and primary radicals with the more stable tertiary radical being favoured in each case. The difference in product distributions is explained by the greater reactivity, and therefore lower selectivity, of the Cl radicals. The - abstraction step for chlorination is exothermic and fast, so the transition state is early and has little radical character. For bromination the T.S. is more like the radical so the system can sense which type of radical is formed with tertiary being greatly favoured. 6

153 Chem1 Practice Problems Dr. Peter Norris, 2014

154 Dr. Peter Norris Chem 1 Klein Chapter 1 Problems : Review of General Chemistry 1. Draw viable structures for molecules with the following molecular formulae. Remember that each atom has a standard valence when forming neutral molecules, for example halogens and are monovalent, is divalent, N is trivalent, and C is tetravalent. Each of the molecules has only single bonds between atoms. 2. Draw Lewis formula structures for molecules with the following molecular formulae. Show all single bonds as single lines and any lone pairs where appropriate. 3. Draw structures for the following molecules that include any formal charges and lone pairs where needed. Each of the molecules has either single bonds or double bonds between atoms and there may be ionic bonds involved in some of the structures. 4. Indicate the hybridization of each of the C, N, and atoms in the following molecules. 5. Draw a structural formula for each of the following molecules and then, using the δ+/δ- convention, label any dipoles that are present each molecule. 1

155 Dr. Peter Norris Chem 1 Klein Chapter 1 Problems : Review of Gen Chem Answers 1. Draw viable structures for molecules with the following molecular formulae. Remember that each atom has a standard valence when forming neutral molecules, for example halogens and are monovalent, is divalent, N is trivalent, and C is tetravalent. Each of the molecules has only single bonds between atoms. a. C 3 Cl b. C 2 5 F c. C 2 6 d. C 3 7 C Cl C C F C C C C C or or C C C C C e. C 2 4 Cl 2 f. C 2 3 F 3 g. C 3 8 h. C 2 4 Cl C C Cl Cl C F C F F C C C C C Cl or or or Cl C C Cl F C F C F Cl C C 2. Draw Lewis formula structures for molecules with the following molecular formulae. Show all single bonds as single lines and any lone pairs where appropriate. 1

156 Dr. Peter Norris Chem 1 3. Draw structures for the following molecules that include any formal charges and lone pairs where needed. Each of the molecules has either single bonds or double bonds between atoms and there may be ionic bonds involved in some of the structures. 4. Indicate the hybridization of each of the C, N, and atoms in the following molecules. 5. Draw a structural formula for each of the following molecules and then, using the δ+/δ- convention, label any dipoles that are present each molecule. 2

157 Dr. Peter Norris Chem 1 Klein Chapter 2 Problems : Molecular Representations 1. Turn each of the following bond-line structures into more expanded representations in which each of the C, N,, and atoms are shown. 2. From Table 2.1 in the Klein text, identify all of the functional groups present in the following molecules. 3. Add any missing lone pairs to the following line structures. 4. Draw a second resonance form for each of the following structures. 1

158 Dr. Peter Norris Chem 1 Klein Chapter 2 Problems : Molecular Representations Answers 1. Turn each of the following bond line structures into more expanded representations in which each of the C, N,, and atoms are shown. 2. From Table 2.1 in the Klein text, identify all of the functional groups present in the following molecules. 3. Add any missing lone pairs to the following line structures. 1

159 Dr. Peter Norris Chem 1 4. Draw a second resonance form for each of the following structures. 2

160 Dr. Peter Norris Chem 1 Concepts Klein Chapter 3 : Acids and Bases Worksheet The interaction of a protic acid with a base is the first actual chemical reaction that we study in We use it to introduce some of the fundamental concepts of mechanism, i.e. how to describe the bond-breaking and bond-forming events that occur as a starting material (left-hand side of the equation) is converted to product (right-hand side of the equation). Since we use acids and bases on many occasions as reagents throughout 3719 and 3720, it is important that you know what constitutes an acid or a base and what happens when the two interact. Definitions: Acids donate protons (onsted definition) or accept electrons (Lewis definition) Bases accept protons (onsted definition) or donate electrons (Lewis definition) General Chem: In this case Cl is the acid (proton donor), water is the base (electron donor, proton acceptor) and the green arrows show the proton being transferred to generate the conjugate acid ( 3 + ) and the conjugate base (Cl - ). The strength of the acid in water is measured by the dissociation constant (K a ); the larger the K a, the stronger the acid. In other words, the stronger the acid, the more the above reaction goes to the right. Since the values of K a can range from very large to very small, we use the pk a scale to give manageable numbers (pk a = -log 10 K a ). The pk a range for acids used in rganic Chemistry are in the range 10 (very strong acid) to +50 (very weak acid). pk a values from class (Table 3.1 in Klein text): I,, Cl, 2 S 4 5 to 10 extremely strong acids C 3 C weak acid 2, R weaker acids N 3 38 very weak acid C 4 50 not at all acidic For the most part in 3719 and 3720 we will not be using water as the base; rather we will use some organic or inorganic base which has been chosen to deprotonate the acid to a particular extent. Since we know something about relative acid strength from pk a values, we also know a lot about the relative (conjugate) base strengths: The task in rganic Chemistry is to decide what happens in terms of the equilibrium position when a particular acid is mixed with a particular base. If you understand this, then you can decide which acid or base to use in particular circumstances. The problems on the next page will give you practice with these ideas. 1

161 Dr. Peter Norris Chem 1 1. For each of the following mixtures, complete the equation, then identify the acid and base on the left and the conjugate acid and conjugate base on the right. Comparing acid and base strengths (from pk a values) decide whether the reaction is a) likely to happen at all, b) whether equilibrium will be established, and c) if equilibrium is established which side is favoured? 2. The equilibrium idea means that if the reaction is reversible there will be four species in solution at one time, the acid, the base, the conjugate acid, and the conjugate base. Sometimes this is what is required, but at other times we need to choose bases that will completely deprotonate every molecule of acid, i.e. send the reaction completely to the right. These bases will include C 3 C 2 C 2 C 2 Li, NaN 2, and LiN(i-Pr) 2. Weaker bases will include Na, NaC 3, KtBu, and NaC 2 C 3. For each of these bases, give the products formed when they react with 2, then use pk a values to get an idea of the relative base strengths of these compounds. 3. In Chem 2 we will study reactions based on the deprotonation of ketones such as acetone, (C 3 ) 2 C=, which has a pka of 19. Given the bases LiN(i-Pr) 2 and NaC 3, decide which will be useful to completely deprotonate acetone, and which will be useful for setting up an equilibrium. Explain your choices. 4. Give the products from the following acid-base reactions and identify the acid and base on the left side, as well as the conjugate acid and conjugate base on the right side of the equation. + Na + NaN 2 + C 3 Li 5. For each of the reactions in question 1 and question 4, which will have an equilibrium constant (K) greater than 1, close to 1, or less than 1? Explain your answers. 6. Draw the structure of the conjugate base that will be formed when 1 mole of C 2 C 2 C 2 reacts with 1 mole of C 3 C 2 C 2 C 2 Li. 7. The careful choice of an appropriate solvent will play a major role in whether organic reactions will be successful. For example, reagents such as C 3 Li and NaN 2 will be incompatible with solvents such as water and ethanol. Why is this? 2

162 Dr. Peter Norris Chem 1 Klein Chapter 3 : Acids and Bases Worksheet Answers 1. For each of the following mixtures, complete the equation, then identify the acid and base on the left and the conjugate acid and conjugate base on the right. Comparing acid and base strengths (from pk a values) decide whether the reaction is a) likely to happen at all, b) whether equilibrium will be established, and c) if equilibrium is established which side is favoured? For this type of question you have to know the approximate pk a values discussed in class and have an idea of what they mean in terms of relative acid strength and also relative base strength. a. ere we have two acids of similar strengths (1 butanol on the left and 2 on the right) and therefore two bases of similar strengths. In this situation, the forward reaction is favoured to about the same extent as the reverse reaction. Therefore a) the reaction left to right is likely to happen, b) equilibrium will be established, and c) the equilibrium lies approximately in the middle (similar acid strengths, similar base strengths on both sides of the equation). b. In this example we have acids of very different strength, the carboxylic acid on the left (pk a ~5) is very much stronger than the ammonia on the right (pk a ~38) therefore the left to right reaction is very much favoured. The reverse reaction however is unlikely to occur since the base on the right is far too weak to deprotonate such a weak acid as N 3. Therefore a) the reaction left to right will happen, b) equilibrium will not be established, and c) the right hand side is completely favoured. c. ere we have a situation in which the reaction will go to the right. The C 3 C 2 C 2 C 3 is such a weak acid (pka~50) that it is impossible to deprotonate. A 28 unit pk a difference between acids means that this is a completely irreversible reaction. Therefore a) the reaction from left to right will occur to give the products shown above, b) there will be no equilibrium established, and c) the right hand side would be completely favoured in this case. 2. The equilibrium idea means that if the reaction is reversible there will be four species in solution at one time, the acid, the base, the conjugate acid, and the conjugate base. Sometimes this is what is required, but at other times we need to

163 Dr. Peter Norris Chem 1 choose bases that will completely deprotonate every molecule of acid, i.e. send the reaction completely to the right. These bases will include C 3 C 2 C 2 C 2 Li, NaN 2, and LiN(i Pr) 2. Weaker bases will include Na, NaC 3, KtBu, and NaC 2 C 3. For each of these bases, give the products formed when they react with 2, then use pk a values to get an idea of the relative base strengths of these compounds. C 3 C 2 C 2 C 2 Li + 2 C 3 C 2 C 2 C 3 + Li completely to the right very strong base acid C.A. C.B. pk a ~16 pk a ~50 NaN N 3 + Na completely to the right very strong base acid C.A. C.B. pk a ~16 pk a ~38 LiN(i-Pr) N(i-Pr) 2 + Na completely to the right very strong base acid C.A. C.B. pk a ~16 pk a ~38 Na Na equilibrium, roughly in the middle strong base acid C.A. C.B. pk a ~16 pk a ~16 NaC C 3 + Na equilibrium, roughly in the middle strong base acid C.A. C.B. pk a ~16 pk a ~16 Kt-Bu + 2 t-bu + Na equilibrium, slightly to the right strong base acid C.A. C.B. pk a ~16 pk a ~18 NaC 2 C C 2 C 3 + Na equilibrium, roughly in the middle strong base acid C.A. C.B. pk a ~16 pk a ~16

164 Dr. Peter Norris Chem 1 3. In Chem 2 we will study reactions based on the deprotonation of ketones such as acetone, (C 3 ) 2 C=, which has a pk a of 19. Given the bases LiN(i Pr) 2 and NaC 3, decide which will be useful to completely deprotonate acetone, and which will be useful for setting up an equilibrium. Explain your choices. In this question you have to set up the equation and then decide whether the base employed is indeed strong enough to completely deprotonate the acid, i.e. send the reaction completely to the right. ere (above) we have a very powerful base (very weak conjugate acid) and this reaction will proceed all the way over to the right, i.e. all of the acid molecules will be deprotonated. In this case (above) we are using a weaker base and even though the left to right reaction is possible, the right to left is also now possible. Equilibrium will be established here which will favour the side that contains the weaker conjugate base, in this case the left hand side. The main consequence of using this type of base here is that we now have some of all four species in solution at once. 4. Give the products from the following acid base reactions and identify the acid and base on the left side, as well as the conjugate acid and conjugate base on the right side of the equation.

165 Dr. Peter Norris Chem 1 5. For each of the reactions in question 1 and question 4, which will have an equilibrium constant (K) greater than 1, close to 1, or less than 1? Explain your answers. 1a) K ~ 1 since acids and bases on each side are of similar strengths; 1b) No equilibrium since the acid and very strong base on the left will send the reaction completely to the right, K > 1; 1c) No equilibrium since the acid and very strong base on the left will send the reaction completely to the right, K > 1; 4a) K > 1 since the stronger acid and base on the left will favour the reaction to the right; 4b) No equilibrium since the reaction will go completely to the right, K > 1; 4c) No equilibrium since the reaction will go completely to the right, K > Draw the structure of the conjugate base that will be formed when 1 mole of C 2 C 2 C 2 reacts with 1 mole of C 3 C 2 C 2 C 2 Li. + C 3 C 2 C 2 C 2 Li Li + C 3 C 2 C 2 C 3 pk a ~16 pk a ~5 The more acidic carboxylic acid proton (pka ~5) will be removed before the less acidic alcohol proton (pka ~16) 7. The careful choice of an appropriate solvent will play a major role in whether organic reactions will be successful. For example, reagents such as C 3 Li and NaN 2 will be incompatible with solvents such as water and ethanol. Why is this? These reagents are very powerful bases so they will be rapidly protonated by the solvents in question and destroyed:

166 Dr. Peter Norris Chem 1 Klein Chapter 4 Problems : Alkanes & Cycloalkanes 1. Provide accurate names for each of the following alkanes. You may use either IUPAC or trivial names for any substituents within these molecules. 2. Draw Newman projections for each of the following situations. a. The highest energy conformation of 3-methylnonane along the C-4 C-5 bond axis b. The lowest energy conformation of trans-1-isopropyl-2-propylcyclohexane along the C-1 C-2 axis c. The lowest energy conformation of 7-ethyl-2,3,8-trimethyldecane along the C-5 C-6 bond axis 3. Draw appropriate diagrams for each of the following situations and explain your choices. a. The most stable chair conformation of 1,3-di-tert-butylcylcohexane b. The less stable chair conformation of trans-1-isopropyl-4-methylcyclohexane c. The less stable isomer of 1,2-di-isopropylcyclobutane 4. Indicate which species/conformation is more stable in each of the following situations and give a few words of explanation for your choices. 1

167 Dr. Peter Norris Chem 1 Klein Chapter 4 Problems : Alkanes & Cycloalkanes Answers 1. Provide accurate names for each of the following alkanes. You may use either IUPAC or trivial names for any substituents within these molecules. 2. Draw Newman projections for each of the following situations. a. The highest energy conformation of 3-methylnonane along the C-4 C-5 bond axis b. The lowest energy conformation of trans-1-isopropyl-2-propylcyclohexane along the C-1 C-2 axis c. The lowest energy conformation of 7-ethyl-2,3,8-trimethyldecane along the C-5 C-6 bond axis 1

168 Dr. Peter Norris Chem 1 3. Draw appropriate diagrams for each of the following situations and explain your choices. a. The most stable chair conformation of 1,3-di-tert-butylcylcohexane b. The less stable chair conformation of trans-1-isopropyl-4-methylcyclohexane c. The less stable isomer of 1,2-di-isopropylcyclobutane 4. Indicate which species/conformation is more stable in each of the following situations and give a few words of explanation for your choices. a. b. C 2 C 3 C 2 C 3 or or C(C 3 ) 2 C(C 3 ) 2 aving the two large groups on opposite sides of the ring will avoid destabilizing interactions Both of the large substituents will be able to be in axial positions thereby avoiding 1,3-diaxial problems c. d. C 3 C 3 or C 3 or C 3 C 3 C 3 The right-hand conformation has only one C 3 -C 3 gauche interaction as opposed to two on the left 2 Both of the large substituents will be able to be as far away as possible from each other when in the anti orientation

169 Dr. Peter Norris Chem 1 Klein Chapter 5 Problems : Stereoisomerism 1. Identify any chiral carbons in the following molecules and, using the Cahn-Ingold-Prelog rules, label their configuration as either R or S. 2. Within each of the following pairs of molecules, identify the relationship between them as being either enantiomers, diastereomers, or identical. 3. Convert each of the following structures as directed. 4. Identify all the chiral carbon atoms in cholesterol (below) and label them as either the R or S configuration. 1

170 Dr. Peter Norris Chem 1 Klein Chapter 5 Problems : Stereoisomerism Answers 1. Identify any chiral carbons in the following molecules and, using the Cahn-Ingold-Prelog rules, label their configuration as either R or S. 2. Within each of the following pairs of molecules, identify the relationship between them as being either enantiomers, diastereomers, or identical. 3. Convert each of the following structures as directed. 1

171 Dr. Peter Norris Chem 1 4. Identify all the chiral carbon atoms in cholesterol (below) and label them as either the R or S configuration. 2

172 Dr. Peter Norris Chem 1 Klein Chapter 6 Problems : Reactivity & Mechanisms 1. In each of the following situations, indicate whether the reactions are favoured or disfavoured in terms of enthalpic and entropic factors in the Gibbs free energy equation (Table 6.1 might help here). 2. Draw a mechanistic interpretation (using curved arrow(s) to show bonds forming and breaking), and then an approximate transition state (including partial electron-densities) for each of the following events. 3. Draw curved arrows to describe each of the steps in the following reaction mechanism, and then label those steps as being one of the four types discussed in class, i.e. nucleophilic attack, loss of a leaving group, proton transfer, or rearrangement. Then draw a transition state for each step within the mechanism, and finally indicate which step is rate-determining and the molecularity (unimolecular, bimolecular, etc.) of that step. 1

173 Dr. Peter Norris Chem 1 Klein Chapter 6 Problems : Reactivity & Mechanisms Answers 1. In each of the following situations, indicate whether the reactions are favoured or disfavoured in terms of enthalpic and entropic factors in the Gibbs free energy equation (Table 6.1 might help here). 2. Draw a mechanistic interpretation (using curved arrow(s) to show bonds forming and breaking), and then an approximate transition state (including partial electron-densities) for each of the following events. 1

174 Dr. Peter Norris Chem 1 3. Draw curved arrows to describe each of the steps in the following reaction mechanism, and then label those steps as being one of the four types discussed in class, i.e. nucleophilic attack, loss of a leaving group, proton transfer, or rearrangement. Then draw a transition state for each step within the mechanism, and finally indicate which step is rate-determining and the molecularity (unimolecular, bimolecular, etc.) of that step. Cl Cl A. proton transfer Cl D. nucleophilic attack C. rearrangement 2 B. loss of leaving group 2 Cl carbocation formation is rate-determining and this step is unimolecular Transition states: A. B. + - Cl + + C. D Cl 2

175 Dr. Peter Norris Chem 1 Klein Chapter 7 Problems : Substitution Reactions 1. Provide each of the following alkyl halides with acceptable names. You may use either the functional class or substitutive nomenclature as appropriate. Be sure to assign the configurations of any chiral centers. 2. Draw detailed mechanisms for the following reactions that use curved arrows to show the breaking and forming of bonds and identify the mechanism that is operating. 3. Provide the products expected to be formed under each of the following sets of conditions. 1

176 Dr. Peter Norris Chem 1 Klein Chapter 7 Problems : Substitution Reactions Answers 1. Provide each of the following alkyl halides with acceptable names. You may use either the functional class or substitutive nomenclature as appropriate. Be sure to assign the configurations of any chiral centers. 2. Draw detailed mechanisms for the following reactions that use curved arrows to show the breaking and forming of bonds and identify the mechanism that is operating. a. b. 3 C 3 C I 2 + S N 1 stepwise via 3 o cation CN C C NaCN DMF CN S N 2 - inversion of stereochemistry during concerted substitution c. d. S C 3 DMS SC 3 C S N 2 - backside attack on simple methyl electrophile 1 C 3 C 3 2 Cl S N 1 stepwise with rearrangement Cl C 3 3 C C 3

177 Dr. Peter Norris Chem 1 3. Provide the products expected to be formed under each of the following sets of conditions. 2

178 Dr. Peter Norris Chem 1 Klein Chapter 8 Problems : Elimination Reactions 1. Provide each of the following alkene-containing molecules with acceptable names. Be careful to assign the configurations of any chiral centers (R or S) and double bonds (E or Z). 2. Draw detailed mechanisms for the following reactions that use curved arrows to show the breaking and forming of bonds and identify the mechanism that is operating. 3. Provide the products expected to be formed under each of the following sets of conditions. 1

179 Dr. Peter Norris Chem 1 Klein Chapter 8 Problems : Elimination Reactions Answers 1. Provide each of the following alkene-containing molecules with acceptable names. Be careful to assign the configurations of any chiral centers (R or S) and double bonds (E or Z). 2. Draw detailed mechanisms for the following reactions that use curved arrows to show the breaking and forming of bonds and identify the mechanism that is operating. a. 3 C C 3 C 3 + C 3 + Na E2 with small base favours the trisubstituted (Zaitsev) product b. 2 S 4 heat E1 with acid favours the trisubstituted (Zaitsev) product

180 Dr. Peter Norris Chem 1 c. Cl KtBu TF + tbu + KCl tbu E2 with large base favours the less-substituted (ofmann) product d. 3 P 4 heat + 2 E1 with migration to the tetrasubstituted (Zaitsev) product o cation 2 o cation 3. Provide the products expected to be formed under each of the following sets of conditions. 2

181 Dr. Peter Norris Chem 1 Klein Chapter 9 Problems : Addition Reactions 1. Draw detailed mechanisms for the following reactions that use curved arrows to show the breaking and forming of bonds and identify the mechanism that is operating. 2. Provide the major and minor products expected to be formed under each of the following sets of conditions. 3. Provide the reagents and conditions required to facilitate the following synthetic conversions. 1

182 Dr. Peter Norris Chem 1 Klein Chapter 9 Problems : Addition Reactions Answers 1. Draw detailed mechanisms for the following reactions that use curved arrows to show the breaking and forming of bonds and identify the mechanism that is operating. a. dil. 2 S 4 racemic Electrophilic addition of water with rearrangement 2 o cation prochiral 3 o cation b. C 3 C 2 achiral Electrophilic addition of (hydrohalogenation) via the more stable tertiary cation c. 3 C B 1. B 2. Na, C racemic syn add'n ydroboration-oxidation via concerted addition followed by concerted rearrangement 3 C B 3 C B 3 C B migration with retention 1

183 Dr. Peter Norris Chem 1 2. Provide the major and minor products expected to be formed under each of the following sets of conditions. 3. Provide the reagents and conditions required to facilitate the following synthetic conversions. 2

184 Dr. Peter Norris Chem 1 Klein Chapter 10 Problems : Alkynes 1. Draw detailed mechanisms for the following reactions that use curved arrows to show the breaking and forming of bonds and identify the mechanism that is operating. 2. Provide the major and minor products expected to be formed under each of the following sets of conditions. 3. Provide complete names for the following alkyne-containing molecules, including any R/S or E/Z descriptors. 1

185 Dr. Peter Norris Chem 1 Klein Chapter 10 Problems : Alkynes Answers 1. Draw detailed mechanisms for the following reactions that use curved arrows to show the breaking and forming of bonds and identify the mechanism that is operating. a. excess NaN 2 N 2 TF concerted "E2" concerted "E2" N 2 b. mixture of E/Z alkenes 1. NaN 2 2. C 3 C 2 N 2 S N 2 deprotonation acetylide anion c. 2 S 4, 2 protonation alkyne hydrolysis including enol-keto tautomerism deprotonation Ketone 2 2 trap cation 2 deprotonation Enol protonation 1

186 Dr. Peter Norris Chem 1 2. Provide the major and minor products expected to be formed under each of the following sets of conditions. 3. Provide complete names for the following alkyne-containing molecules, including any R/S or E/Z descriptors. 2

187 Dr. Peter Norris Chem 1 Klein Chapter 11 Problems : Radical Reactions 1. Draw detailed mechanisms for the following reactions that use curved arrows to show the breaking and forming of bonds and any important resonance structures. Then identify the mechanism that is operating. 2. Provide the major products expected to be formed under each of the following sets of conditions. 3. Draw all of the possible resonance structures for the following radicals. 1

188 Dr. Peter Norris Chem 1 Klein Chapter 11 Problems : Radical Reactions Answers 1. Draw detailed mechanisms for the following reactions that use curved arrows to show the breaking and forming of bonds and any important resonance structures. Then identify the mechanism that is operating. a. 3 C 2, h 3 C radical abstraction initiation 2 C 3 C 3 or termination propagation b. 2 C NBS, heat C 2 N initiation termination C 2 propagation or C 2 C 2 C 2 C 2 delocalized benzylic radical 1

189 Dr. Peter Norris Chem 1 c., 2 2 anti-markovnikoff product radical addition abstraction 3 o radical d. 2 2, heat initiation propagation propagation etc. 2

190 Dr. Peter Norris Chem 1 2. Provide the major products expected to be formed under each of the following sets of conditions. 3. Draw all of the possible resonance structures for the following radicals. a. C 2 C 2 C 2 C 2 C 2 C 2 b. c. d. 3

191 Dr. Peter Norris Chem 1 Klein Chapter 12 Problems : Synthesis 1. Provide the major products formed from each step in the following reaction sequences. Be careful to include any changes in stereochemistry that may occur. 2. Give a sequence of reagents that would affect the following synthetic conversions. Each problem requires at least two synthetic steps. 3. In each of the following problems, draw a starting material that could be used as a suitable precursor in the conversion to the given product. 1

192 Dr. Peter Norris Chem 1 Klein Chapter 12 Problems : Synthesis Answers 1. Provide the major products formed from each step in the following reaction sequences. Be careful to include any changes in stereochemistry that may occur. a. C 3 1. NBS, heat 2. NaC 3, TF 3 C C 3 3 C 3. 3 C 4. 3., KtBu, TF racemic b. 1. 2, CCl 4 2. excess NaN (quench) 4. NaN 2 5. C 3 C c. 1. 2, h 2. KC 2 C BR BR 2 4. Na, 2 2 racemic E/Z mixture racemic racemic d. C NaC 3, 1. C 3 2. C C 4. 3 C Zn, 2 2. Give a sequence of reagents that would affect the following synthetic conversions. Each problem requires at least two synthetic steps. 1

193 Dr. Peter Norris Chem 1 3. In each of the following problems, draw a starting material that could be used as a suitable precursor in the conversion to the given product. 2

194 Chem 1 Mechanism Flashcards Dr. Peter Norris, 2013

195 Mechanism Basics Chemical change involves bonds forming and breaking; a mechanism describes those changes using curved arrows to describe the electrons involved There are two main types of curved arrow to describe either 2-electron or 1-electron processes Above, the X-Y bond is forming and the Y-Z bond is breaking There are ~100 mechanisms in Chem1 and Chem2

196 Ch.3 Acid-Base Reactions: Lone-Pair Donors & Acceptors I, Cl, N 3, 3 P 4 pka -10 to -5 Super strong acids 3 + pka 1.7 RC 2 pka ~ 5 acids Ph pka ~ 10 get 2, R pka ~ 16 weaker RCC (alkynes) pka ~ 26 RN 2 pka ~ 36 Extremely weak acid RC 3 pka ~ 60 Not acidic at all Lone pair donor + Lone pair acceptor = Acid-Base reaction Rate-determining step is bimolecular (only one step involved) Acid-Base reactions are generally very fast (proton,, is accessible) Acid-Base reactions appear as components of other mechanisms

197 Ch.7 Stereochemical Change in the S N 2 Reaction MeC()Et + X: MeC(X)Et + : reaction coordinate Chiral 2 carbon with leaving group attached; strong nucleophile Rate-determining step is bimolecular (no carbocation formed) Proceeds with backside attack and stereochemical inversion Transition state is described as being trigonal bipyramidal shape

198 Ch.7 Primary Alcohols (& C 3 ) with -Cl/-/-I S N 2 R + X RX + 2 reaction coordinate 1 alcohol (or C 3 ) + -X alkyl halide = S N 2 reaction Rate-determining step is bimolecular (no carbocation formed) Reaction slowed by steric crowding (C 3 > 1 > 2 > 3 ) Concerted process, no reactive intermediate involved

199 Ch.7 Stereochemical Change in the S N 1 Reaction R X R + X R 2 + X reaction coordinate 3 molecule (with leaving group) + nucleophile = S N 1 reaction Rate-determining step is unimolecular = CARBCATIN FRMED Carbocation is planar so is attacked from both sides to give 2 products Chiral starting material gives racemic mixture of enantiomeric products RX + 2

200 Ch.7 Reaction of a Tertiary Alcohol with -Cl/-/-I = S N 1 R X R + X R 2 + X RX + 2 reaction coordinate 3 alcohol + -X alkyl halide = S N 1 reaction Rate-determining step is unimolecular = CARBCATIN FRMED Carbocation stabilized by hyperconjugation (3 > 2 > 1 > C 3 ) Stepwise process, reactive intermediate (carbocation) involved

201 3C 3 C 3 C C 3 C 3 C C 3 C Ch.8 Reaction of 3 /2 Alcohol with 2 S 4 / 3 P 4 E1 2 S 4 or 3 P 4 heat 3 C C 3C C2 (+ 2 ) potential energy regenerated (- 2 ) C3 C 3C C 2 RC 2 CR RC 2 CR RC 2 CR reaction coordinate RC=CR 2 3 or 2 alcohol + 2 S 4 or 3 P 4 alkene = E1 reaction Rate-determining step is unimolecular = CARBCATIN FRMED Carbocation stabilized by hyperconjugation (3 > 2 > 1 > C 3 ) Product distribution is based on relative alkene stability (Zaitsev rule)

202 Ch.8 Reaction of 3 /2 /1 Alkyl alide with Base E2 B B + B- X X + X 3, 2, or 1 alkyl halide + base alkene = E2 reaction Rate-determining step is bimolecular = no intermediate formed Zaitsev outcome based on alkene stability (substitution pattern) Useful, predictable process since no intermediates are formed

203 3 C Ch.9 Electrophilic Addition of -X to Alkenes + C 3 3 C C 3 3 C C 3 RC=CR 2 + X R 2 C-CR 2 + X RC-CR 2 + X R 2 C-CXR 2 RXC-CR 2 reaction coordinate Alkene + -X (X = Cl,, I) gives alkyl halide addition product(s) Two-step process: slower step is carbocation formation utcome based on carbocation stability (Markovnikoff rule) Carbocation formed so rearrangements are a possibility

204 Ch.9 Acid-catalyzed ydration of Alkenes 3 C 3 C C 3 C C C 3 3 C 2 C 3 RC=CR R2C-CR2 + 2 RC-CR R 2 C-C()R 2 R()C-CR 2 reaction coordinate Alkene + dilute 2 S 4 ( 3 + ) gives alcohol addition product(s) Three-step process, the first being slow formation of carbocation Major product formed via more stabilized carbocation (Markovnikoff) Carbocation(s) generated so rearrangements will be possible

205 Ch.9 Addition-xidation ydration of Alkenes Alkene + -BR 2 gives addition based on sterics and electronics First step is concerted syn addition; no intermediate(s) formed Second (oxidation) step retains original C-BR 2 stereochemistry verall outcome is opposite to that obtained using dilute 2 S 4

206 Ch.9 Addition of alogens to Alkenes Attack from opposite side preferred nly anti product indicates that this is not a syn addition pathway ne product only suggests a modified carbocation intermediate Formation of the bromonium ion explains stereochemical outcome Similar reaction with 2 / 2 gives only anti addition of