SPRING 2012 - EXAM 2 - KEY 1. (5) (For the triene shown below, for which double bond(s) is it possible to assign E or Z descriptors? ANSWER: E 2. (5) In the reaction shown below, Pyridine (labeled below) can most accurately be described as: + N O N OH + O O H pyridine ANSWER: A 3. (5) What is the order of acidity of the following organic molecules? The correct answer should list them in order of MOST acidic to LEAST acidic. OH OH OH O OH N O O N O ANSWER: E 4. (15) Answer the following questions by circling either true or false. Circling both answers results in zero points. (a) E1 and Sn1 reactions have at least two transition states in their TRUE FALSE energy profile. TRUE FALSE (b) Doubling both the concentration of the nucleophile and electrophile in an Sn1 reaction doubles the rate of reaction. (c) Carbon skeleton rearrangements are never seen in elimination reactions TRUE FALSE (d) E2 and Sn2 reactions share a common carbocation intermediate. TRUE FALSE (e) Sn2 reactions of secondary alkyl halides with NaI proceed faster in water than in acetone. TRUE FALSE 5. (30) Answer the following questions about the reaction shown below. Br H NaOMe CH3 a) Write the MAJOR organic product(s) of the E2 reaction in the space above. b) Draw the Newman projection, oriented in the only conformation that will allow the above reaction to proceed. Br H Me H c) Circle the answer below that accurately describes the alkene formed in (a) neither E-alkene Z-alkene 2 d) Add, subtract or otherwise change no more than 3 atoms in the electrophile to create a new molecule that will favor an SN2 reaction over an E2 reaction. One possible answer: Br CH3 6. (30) Predict the product(s) of the following reactions as indicated. Be sure to include stereochemistry when appropriate. (a) Predict the major product(s). KOMe N (b) Predict the major acid-catalyzed dehydration product(s). or H2SO4 H2O, heat HO (c) Predict the major substitution product(s). NaCN (xs) Cl DMSO Br 3 CN CN (d) Predict the major substitution product(s). EtOH O O + O (solvolysis) O O MsO (e) Predict the major product(s). Cl EtO Me OTs Cl Me an excess of NaOEt acetone Me Me 7. (30) Fill in the missing boxes with the appropriate reactant, reagent, or product that will allow for the reaction schemes shown below to proceed. (a) ONa + DMSO Br O Sn2 (b) Br KOH OH O O 4 (c) NaCN N3 CN (1R,3R)-1-azido-3-methylcyclopentane KBr NaN3 N3 (1S,3R)-1-azido-3-methylcyclopentane Br 5 8. (30 points) The following reaction proceeds via solvolysis with the product shown as one possible product. In the box provided, write out the complete mechanism for this transformation. Show all intermediates, all appropriate lone pairs, formal charges and curly arrows. Br MeOH solvolysis O Me Br MeOH solvolysis O Me Me H O H Me 6 O H O Me