Chemistry 3719, Fall 2012 Exam 1 Name: Student number:

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1 Chemistry 3719, Fall 2012 Exam 1 Name: Student number: 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. 1

2 2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or common names for substituents. a. Cl 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. ground state 3 C C Energy hybridize Explain briefly why hybrid orbitals are necessary here: 2

3 4. (12 pts) Give the products expected from each of the following acid-base reactions. Then label each acid with an approximate pka and indicate whether products, reactants, or neither are favoured in each case. a. C 2 + C 3 C 2 K b. C C + LiN[C(C 3 ) 2 ] c. + C 3 Na 5. (8 pts) Provide a complete mechanism for the following reaction that includes curved arrows to denote the making and breaking of bonds. Indicate the rate-determining step for this process. 3

4 6. (6 pts) Complete the following structures by adding any needed formal charges. 7. (6 pts) Draw a second resonance structure and an overall hybrid for each of the following species. a. 3 C b. C N N c. C 3 C 2 8. (6 pts) Show the oxidation number for each C atom in the following reactant and product, and then indicate whether each C atom is oxidized, reduced, or neither in the reaction. 4

5 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. 10. (9 pts) Draw Newman depictions that correspond to the following conformations. 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

6 11. (9 pts) Rank the following species as indicated: 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. 6

7 Chemistry 3719, Fall 2012 Exam 1 - Key Name: Student number: 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. cyclopentane C 3 cis-1,2-dimethylcyclopropane C 3 C 3 C 3 methylcyclobutane trans-1,2-dimethylcyclopropane C 3 3 C C 3 1,1-dimethylcyclopropane C 2 C 3 ethylcyclopropane 1

8 2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or common names for substituents. 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. ground state 3 C C Energy hybridize sp 3 sp 2 p Explain briefly why hybrid orbitals are necessary here: The most obvious reason is that the lone pairs in the ground state structure are not equivalent; the hybridization model fixes that. 2

9 4. (12 pts) Give the products expected from each of the following acid-base reactions. Then label each acid with an approximate pka and indicate whether products, reactants, or neither are favoured in each case. 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 favoured pka ~26 Na c. + C 3 Na + C 3 pka ~16 neither f avoured pka ~16 5. (8 pts) Provide a complete mechanism for the following reaction that includes curved arrows to denote the making and breaking of bonds. Indicate the rate-determining step for this process. C 3 C 3 C 3 C 2 C C 3 C 2 C + 2 C 3 C 3 C 3 C 3 rate-determining C 3 C 2 C 2 C 3 C 2 C C 3 C 3 3

10 6. (6 pts) Complete the following structures by adding any needed formal charges. a. C N b. N c. C S 7. (6 pts) Draw a second resonance structure and an overall hybrid for each of the following species. a. 3 C 3 C 3 C b. C N N C N N C N N C 3 C 3 C 3 c. C 2 C 2 C 2 8. (6 pts) Show the oxidation number for each C atom in the following reactant and product, and then indicate whether each C atom is oxidized, reduced, or neither in the reaction. 4

11 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. cis isomer 3 C C 3 C C 3 C 3 3 C C 3 C C 3 Lots of 1,3-diaxial interactions which make this chair form less stable C 3 both large groups are equatorial, no significant 1,3-diaxial interactions trans isomer C 3 C C 3 C 3 3 C C 3 C Larger group axial so significant 1,3-diaxial interactions that will destabilize this form C 3 C 3 3 C larger group equatorial therefore minimizing 1,3-diaxial problems cis isomer more stable overall since both groups are able to be equatorial minimizing 1,3-diaxial problems 10. (9 pts) Draw Newman depictions that correspond to the following conformations. 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

12 11. (9 pts) Rank the following species as indicated: 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. a. Na vs. Na Charge delocalized in phenoxide ion therefore more stable than the localized charge in the alkoxide ion b. vs. Both large groups are able to be equatorial in this isomer thereby avoiding 1,3-diaxial interactions c. Li vs. NLi Charge is situated on the more electronegative atom and therefore more stabilized than on N 6

13 Chemistry 3719, Fall 2012 Exam 2 Name: Student number: 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. a. 3 C C 3 or C 3 in electrophilic addition b. or D D in E2 elimination c. or in S N 2 substitution 1

14 2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or common names for substituents. 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. 2

15 4. (8 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. 5. (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. 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. 3

16 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. P.E. reaction coordinate 8. (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. 4

17 9. (15 pts) Give the ultimate major product expected in each of the following situations. a Zn, 2 b. 2,heat c. C 3 C 3 d. 2 in 2 e. C 3 C 3 2,Pd 5

18 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. 11. (6 pts) Provide the reagents required to complete the following transformations. 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. 6

19 Chemistry 3719, Fall 2012 Exam 2 - Key Name: Student number: 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. a. 3 C C 3 or C 3 in electrophilic addition would produce 3 o carbocation as opposed to secondary b. or D D in E2 elimination C- bonds are weaker and therefore easier to break c. or in S N 2 substitution Primary carbon is much more accessible than tertiary 1

20 2. (9 pts) Give each of the following organic molecules an acceptable name. You may use either systematic or common names for substituents. a. (Z)-5-bromo-7-methyloct-4-en-2-ol F F b. 4,4-difluoro-3-propylcyclohex-2-enol c. Cl I (Z)-4-chloro-5-iodo-2-methyloct-4-ene 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. 2 2 S 4, 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

21 4. (8 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. 1-bromo-2-cyclopentylcycloheptane 5. (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. C 3 C 2 C 3 C 2, heat C 3 C 2 C 3 C C 3 C 3 C 3 C 3 C 3 C 2 C C 3 C 2 C C 3 C 3 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. C The better the possible carbocation, the faster the S N 1 reaction; 3 > 2 > 1 > C 3 3

22 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. P.E. A B C A = + - B = + + C = + - reaction coordinate 8. (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. C 2 C 3 B C 2 C 3 B Na 2 2 C 2 C 3 C 2 C 3 B Since and B add to same side of substrate this is a syn addition which must be concerted C 2 C 3 B Since the stereochemistry of the group is the same as the B, this must involve a concerted migration step 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. 4

23 9. (15 pts) Give the ultimate major product expected in each of the following situations. 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 5

24 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. 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) Provide the reagents required to complete the following transformations. 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. 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

25 Chemistry 3719, Fall 2012 Exam 3 Name: Student number: 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. 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 C 2 Cl F 1

26 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. a. F b. Cl F c. C 3 3. (8 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. 2

27 4. (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. a C S 2 Cl pyridine 2. NaCN, DMF b. C C 1. NaN 2,DMF 2. C 3 C 2 C 2 c. I C 3 d. NaC 3,DMF e. C 2 I 1. NaN 3,DMS 2. 2,Pd C 3 3

28 5. (8 pts) Provide the major product expected under the following reaction conditions, and then give a detailed mechanism (using curved arrows) that describes its formation. 6. (8 pts) The following solvolysis conditions give two major products in equal amounts but, 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. 7. (6 pts) Rank the following in decreasing order of reaction as nucleophiles in S N 2 reactions (4 = fastest, 1 = slowest) and then give a brief explanation for your choices. 4

29 8. (8 pts) The following conditions induce a free radical halogenation process at the allylic position with only two products forming with a combined [ ] D = 0; give a mechanistic explanation for this observation. 9. (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. 5

30 10. (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. 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. a. to Fischer b. Cl F C 3 to Wedge-Dash 12. (7 pts) Typical S N 1 and S N 2 reactions are promoted by different types of solvents, namely polar protic and polar aprotic, respectively. Describe two solvents used for S N 1, two for S N 2, and then explain your choices. 6

31 Chemistry 3719, Fall 2012 Exam 3 Key Name: Student number: 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. a. (R) (R) and C 3 (S) (R) C 3 diastereomers b. C 3 (S) (S) C 3 and C 3 (S) (S) C 3 equivalent c. C 2 Cl (R) (S) F C 3 and 3 C (R) (S) C 2Cl F enantiomers 1

32 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. 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. (8 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 Zn, 2 2

33 4. (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. a. 3 C S 2 Cl Ts CN 1. pyridine NaCN, DMF S N 2-inversion b. C C 1. NaN 2,DMF 1. C CNa 2. C C C 2C 2 C 3 2. C 3 C 2 C 2 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 C 3 1. NaN 3,DMS 2. 2,Pd 1. C 2 2. N 3 C 3 2 N C 2 C 3 S N 2 - inversion 3

34 5. (8 pts) Provide the major product expected under the following reaction conditions, and then give a detailed mechanism (using curved arrows) that describes its formation. C C dilute 2 S 4 C C 3 ( + / 2 ) 2 C 2 2 C C C C 6. (8 pts) The following solvolysis conditions give two major products in equal amounts but, 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 Products are actually Flat carbocation, attacked from both sides 2 50/50 R/S diastereomers and not enantiomers so the optical rotations will not cancel each other out. 7. (6 pts) Rank the following in decreasing order of reaction as nucleophiles in S N 2 reactions (4 = fastest, 1 = slowest) and then give a brief explanation for your choices. SNa Na Na RSNa has charge on larger S which is easier to share than (electronegativity); Localized charge on is more reactive (and more nucleophilic) than delocalized charge on carboxylate; neutral carboxylic acid is most stable and least reactive 4

35 8. (8 pts) The following conditions induce a free radical halogenation process at the allylic position with only two products forming with a combined [ ] D = 0; give a mechanistic explanation for this observation. 2 heat initiation propagation or termination 2 propagation The prochiral radical intermediate is delocalized, however the resonance forms are equivalent; the termination or propagation steps lead to the same racemic products 9. (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. Ts NaC 3 C 3 + major minor C 3 Ts KC(C 3 ) 3 C 3 only product In the top reaction the electrophile is secondary and the nucleophile is small; this will all S N 2 to occur with a minor E2 side-product, the alkene. In the bottom reaction the electrophile is tertiary and more crowded which stops the S N 2 from operating. The large nucleophile/base will allow only E2 to occur, in this case to give the conjugated alkene product exclusively. 5

36 10. (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. 1. NaI, acetone 2. Na, DMF 1. I Finkelstein, S N 2 with inversion 3. NaN 2 4. C 3 C 2 I 2. S N 2 with inversion 3. Na Acid-Base reaction 4. C 2 C 3 S N 2 with inversion 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. 12. (7 pts) Typical S N 1 and S N 2 reactions are promoted by different types of solvents, namely polar protic and polar aprotic, respectively. Describe two solvents used for S N 1, two for S N 2, and then explain your choices. S N 1 reactions work best in polar protic solvents, which are capable of -bonding to leaving groups and then facilitating their departure. These polar solvents will also help stabilize the transition states and the carbocation formed during this process, and will ultimately serve as the nucleophile in such solvolysis reactions. In S N 2 reactions the -bonding ability of polar protic solvents is a disadvantage since that reduces nucleophile reactivity; polar aprotic solvents solubilize the reagents but do not attenuate their reactivities. Polar aprotic solvents will stabilize polar bimolecular transition states while not interfering as nucleophiles themselves. 6

37 Chemistry 3719, Fall 2006 Exam 1 Name: Student number: 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) Draw a second resonance structure for each of the following anions. a. C N b. C S c. 1

38 2. (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 which side of each equation is favored. a. C 3 C CLi + 2 b. + Na c. N 2 + C 3 C 2 C 2 Li d. + NaN 2 e. + C 3 CK 2

39 3. (5 pts) Which of the two molecules below is the stronger acid? Give their approximate pka values and explain your choice in terms of the relative stabilities of the respective conjugate bases. 4. (12 pts) Draw Newman projections that correspond to each of the following: a. The lowest energy conformation of n-nonane looking down the C3 C4 bond axis. b. A gauche conformation of 1-bromo-3-fluoropropane looking down the C1 C2 bond axis. c. The least stable conformation of 2-methylheptane along the C4 C5 bond axis. 3

40 5. (5 pts) Give the hybridization of each of the highlighted atoms in the following molecules (sp 3, sp, etc.). C C C C 3 C C C 3 6. (10 pts) The following questions relate to the cis and trans- isomers of 1-fluoro-2-isopropylcyclohexane. a. Draw two ring-flipped conformations of the cis-isomer and circle the more stable of the two. b. Draw two ring-flipped conformations of the trans-isomer and circle the more stable of the two. c. Using Newman projection terminology; what is the relationship between the fluoro and isopropyl groups in the least stable of all of the conformations you have drawn above (one word answer)? 4

41 7. (20 pts) Provide acceptable names for the following compounds. a. Cl C(C 3 ) 2 b. Cl c. d. C 3 C 3 e. F 5

42 8. (6 pts) For the highlighted atom in each of the following molecules fill in the ground state electron configuration (i.e from the Periodic Table) in the given orbitals (the horizontal lines). Then draw a picture, on the right, of the hybridization model that best explains the bonding in the highlighted atoms. C Energy hybridize Energy hybr idize 9. (6 pts) Circle any of the following that are 2 o alcohols or alkyl halides. Cl C 3 C 2 C()C 3 F C(C 3 ) 2 C 3 C 3 6

43 10. (15 pts) Draw acceptable structures for each of the following molecules. a. cis-1-cyclopropyl-3-methylcyclohexane b. 3,3,8-trimethyl-1-dodecanol c. trans-1-t-butyl-2-ethylcyclobutane d. 6-ethyl-2,3,5,5-tetramethyldecane e. bicyclo[5.2.0]nonane 7

44 Chemistry 3719, Fall 2006 Exam 1 Key Name: Student number: 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) Draw a second resonance structure for each of the following anions. a. C N C N b. C S C S c. 1

45 2. (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 which side of each equation is favored. a. C 3 C CLi R S + 2 C 3 C C favored pka ~16 pka ~26 + Li b. + Na RS Na + 2 favored pka ~5 pka ~16 c. RS N 2 + C 3 C 2 C 2 Li + NLi favored C 3 C 2 C 3 pka ~36 pka ~60 d. + NaN 2 RS favored Na + N 3 pka ~16 pka ~36 e. + C 3 CK LS favored K + C 3 C pka ~10 pka ~5 2

46 3. (5 pts) Which of the two molecules below is the stronger acid? Give their approximate pka values and explain your choice in terms of the relative stabilities of the respective conjugate bases. pka ~5 pka ~16 base base 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. 4. (12 pts) Draw Newman projections that correspond to each of the following: a. The lowest energy conformation of n-nonane looking down the C3 C4 bond axis. C 2 C 3 Anti (C 2 ) 4 C 3 b. A gauche conformation of 1-bromo-3-fluoropropane looking down the C1 C2 bond axis. F C 2 F Gauche c. The least stable conformation of 2-methylheptane along the C4 C5 bond axis. C 2 C(C 3 ) 2 C 2 C 3 Eclipsed 3

47 5. (5 pts) Give the hybridization of each of the highlighted atoms in the following molecules (sp 3, sp, etc.). C C sp 2 sp sp 3 C C 3 sp 2 C C C 3 sp 6. (10 pts) The following questions relate to the cis and trans- isomers of 1-fluoro-2-isopropylcyclohexane. a. Draw two ring-flipped conformations of the cis-isomer and circle the more stable of the two. C(C 3 ) 2 F F (C 3 ) 2 C Larger group equatorial b. Draw two ring-flipped conformations of the trans-isomer and circle the more stable of the two. F F (C 3 ) 2 C C(C 3 ) 2 Both larger groups equatorial c. Using Newman projection terminology; what is the relationship between the fluoro and isopropyl groups in the least stable of all of the conformations you have drawn above (one word answer)? F ipr Anti 4

48 7. (20 pts) Provide acceptable names for the following compounds. a. Cl C(C 3 ) 2 trans-1-chloro-2-isopropylcyclopentane b. Cl 5-chloro-6-methylheptan-2-ol or 5-chloro-6-methyl-2-heptanol c. 5-tert-butyl-2-ethyl-1-methylcyclooctane d. C 3 C 3 cis-1,4-dimethylcyclohexane e. 2,2-dibromo-5-fluoro-4-methylheptane F 5

49 8. (6 pts) For the highlighted atom in each of the following molecules fill in the ground state electron configuration (i.e from the Periodic Table) in the given orbitals (the horizontal lines). Then draw a picture, on the right, of the hybridization model that best explains the bonding in the highlighted atoms. C Energy hybr idize p(toπ bond) sp 2 (to σ bonds) C:1s 2 2s 2 2p x 1 2p y 1 Energy hybr idize sp 3 (to σ bonds) : 1s 2 2s 2 2p x 2 2p y 1 2p y 1 9. (6 pts) Circle any of the following that are 2 o alcohols or alkyl halides. Cl C 3 C 2 C()C 3 F C(C 3 ) 2 C 3 C 3 6

50 10. (15 pts) Draw acceptable structures for each of the following molecules. a. cis-1-cyclopropyl-3-methylcyclohexane C 3 b. 3,3,8-trimethyl-1-dodecanol c. trans-1-t-butyl-2-ethylcyclobutane C 3 C 2 C(C 3 ) 3 d. 6-ethyl-2,3,5,5-tetramethyldecane e. bicyclo[5.2.0]nonane 7

51 Chemistry 3719, Fall 2006 Exam 2 Name: Student Number: 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 expected major and minor products from the following reaction then give a complete mechanism for how the major product is formed. 2 S 4 1

52 2. (9 pts) Give structures for each of the following molecules. a. 1,3-dichloro-6-isopropylcyclohept-1-ene b. 2-bromo-5-methyl-4-vinylcyclohexanol c. 3-bromo-5-fluorohex-5-en-2-ol 3. (10 pts) Give the major monobrominated product from the following reaction and then show a mechanism that includes all the possible ways how that product is formed during the reaction. 2,heat 2

53 4. (18 pts) Give organic product(s), labeling major and minor where applicable, for the following reactions. a. b. 2,heat c. C 3 3 P 4 C 3 d. C 3 C 3 2,Pt e. NaC 2 C 3 f. 3

54 5. (9 pts) Give a complete mechanism (using curved arrows) for the following reaction. C 3 C 3 6. (8 pts) Provide the expected products in the following reaction and then a detailed mechanism for the formation of the major product only. Explain why the product you chose is major. Cl 4

55 7. (12 pts) Give acceptable names for each of the following molecules. a. b. c. Cl d. F 8. (10 pts) Draw the reaction profile (potential energy vs. reaction coordinate) for the following conversion that includes picture(s) of the transition state(s) involved. NaC 3 Potential energy 5 Reaction coordinate

56 9. (6 pts) Circle the more stable species in each of the following pairs and give a brief explanation of your choices. a. vs. b. vs. c. vs. 10. (9 pts) For each of the following reactions, give the major product expected and then name that product. a. NaC 3 Cl b. Cl c. 2 S 4, 2 6

57 Chemistry 3719, Fall 2006 Exam 2 Name: Student Number: 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 expected major and minor products from the following reaction then give a complete mechanism for how the major product is formed. 2 S 4 + major minor 2 2 1

58 2. (9 pts) Give structures for each of the following molecules. a. 1,3-dichloro-6-isopropylcyclohept-1-ene Cl Cl b. 2-bromo-5-methyl-4-vinylcyclohexanol c. 3-bromo-5-fluorohex-5-en-2-ol F 3. (10 pts) Give the major monobrominated product from the following reaction and then show a mechanism that includes all the possible ways how that product is formed during the reaction. 2,heat 2x 2

59 4. (18 pts) Give organic product(s), labeling major and minor where applicable, for the following reactions. a. + major minor b. 2,heat + major minor C 3 C 3 C 3 c. 3 P 4 + C 3 C 3 C 3 major minor d. C 3 C 3 2,Pt C 3 C 3 only one product (from sy n addition) e. NaC 2 C 3 + major minor f. only one product (via 3 o carbocation) 3

60 5. (9 pts) Give a complete mechanism (using curved arrows) for the following reaction. C 3 C 3 C 3 C 3 C (8 pts) Provide the expected products in the following reaction and then a detailed mechanism for the formation of the major product only. Explain why the product you chose is major. Cl Cl + Cl Cl major minor Cl Major product formed via more stabilized carbocation (Markovnikoff) 4

61 7. (12 pts) Give acceptable names for each of the following molecules. a. 2-isopropenylcyclopentanol b. (E)-6-bromo-4-methylhept-3-ene or trans-6-bromo-4-methylhept-3-ene c. Cl 4-chlorocyclohex-2-enol d. F 3-bromo-5-f luoro-2-methylhex-2-ene 8. (10 pts) Draw the reaction profile (potential energy vs. reaction coordinate) for the following conversion that includes picture(s) of the transition state(s) involved. NaC 3 δ Potential energy δ C 3 E2 Reaction coordinate 5

62 9. (6 pts) Circle the more stable species in each of the following pairs and give a brief explanation of your choices. a. vs. electron-donating alkyl groups help stabilize sp 2 C in alkenes - the more alkyl groups the more stable the alkene (tetra- vs. trisubstituted) b. vs. Electron-deficient radicals are stabilized by the sharing of electron density from adjacent σ bonds (tertiary vs. secondary radical) c. vs. Trans alkene is more stable than the cis isomer here since the alkyl groups attached to the double bond will not interact 10. (9 pts) For each of the following reactions, give the major product expected and then name that product. a. NaC 3 2-methylhex-2-ene Cl b. Cl Cl 1-chloro-3,3-dimethylpentane c. 2 S 4, 2 3-methylheptan-3-ol 6

63 Chemistry 3719, Fall 2006 Exam 3 Name: Student Number: 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) Give the organic product(s) from the following reaction and then discuss the stereochemical outcome in terms of the mechanism that is operating. 2 (cold, dark) 1

64 2. (12 pts) Provide acceptable names for the following molecules that include the appropriate stereochemical descriptors (R/S, cis/trans). a. Cl b. F c. F C 2 Cl C 3 3. (12 pts) Draw structures for each of the following molecules. a. (1R,3R)-3-vinylcyclopentanol b. (1S,2S)-1,2-dibromocyclohexane c. (3R,4S)-4-chlorohex-1-ene-3-ol 2

65 4. (10 pts) Draw all of the possible stereoisomers of 4-bromo-2-hexanol as wedge-dash depictions, then label each stereogenic centre as being either the R or S configuration. Finally, relate the isomers to each other as either enantiomers or diastereomers. 5. (6 pts) Rank the following molecules in terms of how fast they will react with NaN 3 in DMF solution; 1 is the fastest reaction, 4 is the slowest reaction. iefly explain your choices. 3 C C 3 3 C 3

66 6. (18 pts) Give the expected products from the following reactions, labeling major and minor where needed. When more than one set of reagents are given the product(s) from each step is(are) required. a. C C 1. NaN 2 2. C 3 C 2 b. peroxides, c. 1. 2, 2 2. Na d. NaN 3,DMF e Zn, 2 f. 4

67 7. (8 pts) Draw a mechanism for the following portion of the olefin hydroboration/oxidation reaction. B B Na, 2 2 B (6 pts) For the following portion of the ozonolysis reaction, use curved arrows to show a mechanism for how the compound on the left converts to the product on the right. 3 5

68 9. (9 pts) Within each of the following pairs of molecules, identify any stereogenic centres, label them as having the R or S configuration, and then indicate the relationship between the two molecules; are they enantiomers, diastereomers, or are they identical? a. Cl and Cl C 3 C 2 C 3 b. and Cl Cl c. C 3 F and F C 3 C 3 C (7 pts) The following bromide has an optical rotation ([α] D ) of +38. After reaction with water the measured [α] D of the product mixture is found to be 0. Give the products and explain the change in optical rotation in terms of the mechanism and the structure of the intermediate formed during this reaction. 2 6

69 11. (6 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. a. Which of the following species is the better nucleophile? Why? b. Which of the following would react faster with NaCN in DMF? Why? Cl c. Which of the following solvents would allow for faster S N 2 reactions? Why? N C 3 C 3 7

70 Chemistry 3719, Fall 2006 Exam 3 Key Name: Student Number: 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) Give the organic product(s) from the following reaction and then discuss the stereochemical outcome in terms of the mechanism that is operating. δ+ δ- 2 (cold, dark) only trans product formed Isolation of the trans product only suggests that the adds and forms a modified carbocation in which stabilizes by bonding to both carbons of the double bond; the bromide anion can then only approach from the opposite face (here from below) to give the trans product. 1

71 2. (12 pts) Provide acceptable names for the following molecules that include the appropriate stereochemical descriptors (R/S, cis/trans). a. Cl (R)-4-chloro-5,5-dimethylhept-1-ene b. F (1R,3R)-3-fluorocyclooctanol c. F C 2 Cl C 3 (2R, 3S)-2-bromo-2-chloro-3-fluorobutan-1-ol 3. (12 pts) Draw structures for each of the following molecules. a. (1R,3R)-3-vinylcyclopentanol b. (1S,2S)-1,2-dibromocyclohexane c. (3R,4S)-4-chlorohex-1-ene-3-ol Cl 2

72 4. (10 pts) Draw all of the possible stereoisomers of 4-bromo-2-hexanol as wedge-dash depictions, then label each stereogenic centre as being with the R or S configuration. Finally, relate the isomers to each other as either enantiomers or diastereomers. (S) (R) diast. (S) (S) enant. diast. enant. (R) (S) diast. (R) (R) diast. 2 stereogenic centres, therefore 4 (2 n ) possible stereoisomers. No internal symmetry, therefore no meso possibility 5. (6 pts) Rank the following molecules in terms of how fast they will react with NaN 3 in DMF solution; 1 is the fastest reaction, 4 is the slowest reaction. iefly explain your choices. 3 C C 3 3 C The rate of the S N 2 reaction is slowed by local crowding, which makes it more difficult for the nucleophile (N 3 -) to approach the electrophilic carbon. The fastest reaction here will occur with substrate 1, which is a simple 1 system with little extra bulk at the β- and γ-carbon atoms. Substrate 2 has a bulk cyclohexyl group at the γ- carbon, and this bulk increases with the addition of further methyl groups in 3 and 4. 3

73 6. (18 pts) Give the expected products from the following reactions, labeling major and minor where needed. When more than one set of reagents are given the product(s) from each step is(are) required. a. C C 1. NaN 2 2. C 3 C 2 1. C CNa 2. C C b. peroxides, + major c. 1. 2, 2 2. Na d. NaN 3,DMF N 3 e Zn, f. 4

74 7. (8 pts) Draw a mechanism for the following portion of the olefin hydroboration/oxidation reaction. B B Na, 2 2 B B concerted addition B B migration 2 B 8. (6 pts) For the following portion of the ozonolysis reaction, use curved arrows to show a mechanism for how the compound on the left converts to the product on the right. 3 5

75 9. (9 pts) Within each of the following pairs of molecules, identify any stereogenic centres, label them as having the R or S configuration, and then indicate the relationship between the two molecules; are they enantiomers, diastereomers, or are they identical? a. (R) (S) Cl and Cl C 3 (S) (S) C 2 C 3 diastereomers b. (S) (S) and (S) (S) identical Cl Cl c. (S) C 3 F (R) and F (R) C 3 (S) enantiomers C 3 C (7 pts) The following bromide has an optical rotation ([α] D ) of +38. After reaction with water the measured [α] D of the product mixture is found to be 0. Give the products and explain the change in optical rotation in terms of the mechanism and the structure of the intermediate formed during this reaction. 2 + enantiomers The 3 alkyl bromide will produce a planar carbocation during this solvolysis reaction, which is then attacked from either side by the nucleophile, in this case water. The approximately equal chance of attacking either side of the cation leads to approximately equal amounts of enantiomeric products, which explains the observed optical rotation change. 6

76 11. (6 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. a. Which of the following species is the better nucleophile? Why? The circled nucleophile is less stable since the charge is localized, it will therefore be more reactive in substitution reactions than the species on the right in which the charge is delocalized. b. Which of the following would react faster with NaCN in DMF? Why? Cl is a better leaving group than Cl since anion is more stable than Cl anion (size); S N 2 Reactions such as these go faster with better leaving groups. c. Which of the following solvents would allow for faster S N 2 reactions? Why? N C 3 C 3 Polar aprotic solvents work better in S N 2; polar protic, such as the alcohol here, will -bond to the nucleophile thereby forming a solvent coating around the nucleophile; this will slow down its approach to the electrophilic carbon. 7