NAME: SUMMER 2015 MIDTERM

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1 page 1 pts NAME: SUMMER 2015 MIDTERM hemistry 350 Professor: Dr. Gergens take-home portion (DUE at the beginning of the period, 6/16) Do your best on this take-home portion of your midterm. I may grade only selected problems and/or the whole exam. Late midterms will not be accepted. Answers to this midterm will be made available on 6/16 after 7pm. I will provide you a scantron on Tuesday. NLY answers on the scantron and selected problems on this exam will be graded. Knowing the concepts to correctly answers the BNUS questions is a requirement for student success in completing all questions on the follow up exam MT1 next Thursday) 1. The are three isotopes: hydrogen-1, hydrogen-2, and hydrogen-3. omplete the following for Element Symbol Atomic Number Mass Number # of Protons # of Neutrons # of Electrons hydrogen-3 an atomic number of 3 and 0 electrons D. a mass number of 3 and 2 neutrons an atomic number of 1 and mass number of 2 E. a mass number of 3 and 0 neutrons. 1 protons and 1 neutron 2. Which of the species below is more basic than sodium amide, NaN 2. 3 Li, methyl lithium D. both b and c sodium alkoxide, RNa E. all of the above. 3 2 Na, sodium acetate 3. preferred side of equilibrium N + Ph - N + Ph 4.. most basic anion 2 N 2. D. 5. most stable conformer A B 6. the numerical value for the overall G for conformer B going to in question 6? For every 1.36 kcal/mol change in free energy difference, G, at 25, Keq will vary by a factor of D. 10 E most likely to ring "flip" Me Me Me Me Me Me. Me Me D. 9.. affords the most 1,3-diaxial interaction in monosubstituted cyclohexane i-pr n-bu n-pr t-bu Et. D. E.

2 page 2 pts 10. The predicted valence bond theory bond angle in 2 would be less than 90. The actual experimental bond angle in the bond angle in 2 has been experimentally determine to be Which valence bond picture is consistent with the predicted observed bond angle for 2? s 2 orbital configuration 2s 2 2p VBT bondig model For the compound on the right. Pick the best choice for the questions 11-17: 2 1 N The major functional groups in the molecule are 3 amine 1 amine. 3 amine D. 3 amine E. 3 amine ether ketone ester ketone 3 amide 12. ow many non bonding electron pairs are in this molecule? D. 4 E What is the degree of unsaturation in this molecule D. 5 E. greater than What is the hybridization about the atom identified as 1? p sp. sp 2 D. sp 3 E. sp The geometry about the atom identified as 2? tetrahedral trigonal planar. pyramidal D. bent E. linear 16. The bonding molecular orbital(s) the between the = and the atom identified as 3 σ( sp 2 - sp 2 ) 2 σ( sp - sp 2 ) π( p - p). σ( sp 2 - sp 3 ) D. σ( sp - sp 2 ) π( p - p) E. σ( sp - sp) π( p - p) 17. The nitrogen atom is conjugated with the = bond True False. Not enough information

3 page 3 pts 18. Which is the major resonance contributor (form)? D.. D. E. none are valid 19. In the chair conformer, groups and Me are Me both equatorial & cis both axial & cis. both axial & trans D. both equatorial & trans E. axial & equatorial & cis 20. The Lewis acid in the reaction below? S 2 (g) + BF 3 (g) ---> S 2 BF 3 (S) BF 3 is the Lewis acid because boron is trigonal planar having an empty p orbital which is capable of accepting an electron pair. BF 3 is the Lewis acid because boron is trigonal pyramidal having an empty p orbital which is capable of accepting an electron pair.. BF 3 is the Lewis acid because boron is trigonal planar having an empty p orbital which is capable of donating an electron pair. D. S 2 is the Lewis acid because sulfur is bent in geometry having an electron pairs capable of electron pair donation. E. S 2 is the Lewis acid because sulfur is linear in geometry having an electron pairs capable of electron pair donation. 21. Which cation forms the fastest under the reaction? int : Which cation product is most stable? l l.. D. can't be determined E. none are valid 22. most stable carbocation int : Which cation has the most resonance contributors (forms). D. 23. carbocation B above is allylic vinylic benzylic. tertiary D. secondary E. 24. highest boiling N A B D 3

4 page 4 pts Look at the reaction energy diagram shown here for X(g) + Y(g) XY(g) and use it to answer the following questions X + Y XY 25. ow many reactive intermediates are there? D. E. 26. ow many transition states are there? D. E. 27. Which transition state is fastest? D. E. 28. The overall reaction is for (X +Y) going to endothermic exothermic XY is? 29. the numerical value for the overall G for the reaction for (X +Y) going to XY? the numerical value for the overall Keq for the reaction (X +Y) going to XY in the above?. D. E. 31. S for the reaction is predicted to be K eq >1 K eq <1 K eq =0 K eq <-1 K eq = ow many sigma bonds are in 2 N Its degree of unsaturation is equal to D. E D. E. BNUS (questions are BNUS questions, the below concepts are covered in hapters 6 & 7) 34. In the free radical chlorination of methane, the second propagation step in the mechanism is 4 + l ---> 3 + l. l > 3 l l 2 ---> 2 l D. 3 + l 2 ---> 3 l + l 35. least thermodynamically stable double bond least negative heat of hydrogenation, (-) A 3 B substituent w/ highest ranked priority by ahn-ingold-prelog rules A B D 38. Which is the l l Z stereoisomer l l. D.

5 Mantras - (write out our mantra exactly as stated in class; be accurate and precise in your response) page 5 pts a) I say "chemistry", give mantra" b) I say "IA", give mantra" c) "electronegativity", give mantra d) Atoms chemically... (complete this mantra exactly as stated in class) e) Explain in detail why magnesium metal's favorite oxidation state as an ion is 2+. f) I say "reaction," give mantra g) I say "stability," give mantra h) I say "resonance," give mantra i) I say "acid," give mantra j) I say, "conjugate base," give mantra k) pi bond (fill in blank)

6 M Theory page 6 pts 1) Draw the resulting M's formed from the combination of A's and 2) give the resulting M an appropriate M label Acid-Base onjugates omplete by drawing in the corresponding conjugates and any contributing resonance forms: State you MANTR I say "conjugate base," and you say ". (give mantra as stated in class) " N acid A conjugate base A B B Stability Mantra b. ircle the letter for the conjugate which is most stable: A B c. Applying your stability mantra learned in class, give a full explanation for your choice in (b) above.

7 page 7 pts Acid-Base Reactivity a. Draw in ALL carbons and hydrogens onto the line-angle structrue identified as molecule 1. b Draw the specified conjugates, A-D. Include formal charge and resonance contributors where appropriate. c. RANK the lettered conjugates starting with the most stable on the left to the least stable ending the right. PLAE Ranking here: add a proton + to the carbonyl oxygen A add a proton + to the α-carbon to the carbonyl B N 1 add a proton + to the α-carbon to the nitrogen D add a proton + to the nitrogen Structure, Functional Groups & Abbreviations a. Draw the line-angle structure for the substance on the left ( 2 ) 3 ( 3 ) 2 b. Name the bond positions identified as A & B c. Name of the functional groups identified as 1 & Draw the line-angle structure for the abbreviated substances below potassium t-butoxide, tbuk PhiBu

8 page 8 pts Resonance Structures & Arrow Pushing Within a Substance Draw all possible resonance structures for the following substance. Use curved arrows to show the flow of electrons and all formal charges. 3 N Stability a. Give each substance a logical identifiable label (i.e., benyzlic, onium ion, chloronium ion, primary cation, etc.) b. RANK the lettered substances starting with the most stable on the left to the least stable ending the right. c. Give a brief explanation for your overall ranking in b above Acid-Base Reactivity & Arrow Pushing Between Substances For the reactants, complete the reaction for the given arrow push and draw the predicted product formed under the reaction and any contributing resonance forms. 2 + l N N l Which nonbonded pair of electrons is protonated? Draw in the arrow push and complete the reaction. - Which hydrogen is deprotonated by base? Draw in the arrow push and complete the reaction draw the substances formed and any resonance structures

9 page 9 pts Alkane onformation Analysis a. Draw in ( ) all gauche interactions on B &. A is done for you. b. ircle the least stable conformer c. X the least stable conformer. 0.9 kcal mole 3 3 A 0.3 kcal/mole 3 3 B d. Draw the substance's line-angle structure. e. Name the substance: f. The substance is a alkyl halide (circle one) draw line-angle structure name: Bz allylic Me vinyl Ph Like we did in class, draw the Newman projections for the aliphatic shown above about its 2-3 bond in the eclipsed, staggered, and skewed conformations. Use the templates below. Label all gauche interactions and calculate a torsional strain for each conformation. Plot a graph of the torsional strain observed as the aliphatic rotates about the 2-3 bond. Begin with the totally eclipsed conformer with a dihedral angle of zero. Place into the box the total torsional strain for each conformer. Use the thermodyamic data given below. As gauche methyl-bromine interaction is worth 0.3 kcal/mole as shown above torsional eclipsing methyl groups > eclipsing methyl-hydrogen > eclipsing hydrogen-hydrogen strain 3.0 kcal 1.3 kcal 1.0 kcal torsional eclipsing methyl bromine > eclipsing bromine-hydrogen > eclipsing hydrogen-hydrogen strain 2.1 kcal 1.1 kcal 1.0 kcal Energy (kcal/mole) energy (kcal/mole) totally eclisped 5.4. Give labeled names to conformers,,. above

10 page 10 pts ycloalkane onformation analysis omplete this picture for the following equilibrium: a. Draw the chair conformations for the cis-1-hydroxy-4-methylcyclohexane b. ircle the most stable conformer. c. alculate G and K eq at 25 value for the energy value G =, K 25 = A B Newman Projection Template d. Describe mathematically how the free energy difference between the two conformers is calculated. e. alculate the percentage of each conformer present at 25 for you defined equilibrium above? SW YUR WRK FR FULL REDIT. A% & B% f. BNUS - hapter 4 - Draw Newman Projection sighting down 2-1 and 4-5 directly underneath each conformer you drew above using the shown template above, BNUS - hapter 6 Thermodynamics Predict the sign for the given thermodynamic term: S G

11 This entire page is worth BNUS Give labels, identify, complete and name the reactions. onditions (acidic, basic, neutral, oxidizing, reducing, polar protic, polar aprotic, etc.) page 11 pts 2 l reaction name/type 3 2 Na metal 3 -N 2 l 3 - Na Li l BNUS - hapter 7 & 8, omplete the reactions and name the reaction type: reaction name/type reaction name/type 2, 2 l specify stereochemistry 3 RR reaction name/type 1.B 3 TF , reaction name/type specify stereochemistry

12 page 12 pts This entire page is worth BNUS Mechanism a. Name the reaction and state the reaction. b. Give a stepwise mechanism for the following reaction. Your mechanism should show individual steps in the reaction that lead to all the products formed. Use curved arrows and indicate all formal charges reaction name/type c. Draw a representative potential energy curve that correctly shows your mechanism. Label important intermediates and transition states in your mechanism and on your potential diagram. energy reaction time d.alculate for the reation using the given bond dissociations energies (kcals/mol) = BDE (kcal/mole) = e. Describe in words your the individual steps in your mechanism. Be brief, accurate, precise and to the point.