Organic Chemistry 2331H
Fall 2022
EXAM 3
1) (40 points) Consider the pairs of reactions shown below. For each pair, (i) indicate the most likely mechanism, (ii) circle the faster reaction and (iii) provide a brief explanation in precise chemical terms. Note for each pair, assume the same mechanism is operating in both reactions.
2. (40 points) Give the expected major organic product of each of the following reactions. You do not need to indicate stereochemistry.
3) (20 points) When ethyl bromide is added to potassium tert-butoxide, the product is ethyl tert-butyl ether.
a) What is the most likely mechanism type for this reaction? Give the type (SN1, SN2, E1 or E2), not the actual mechanism (no steps or arrows).
b) Sketch a picture of the transition state (TS) for the rate determining step in this reaction. Make it clear what bonds remain largely unaffected in the TS and which bonds are partially formed or broken in the TS.
c) What happens to the reaction rate if the concentration of ethyl bromide is doubled? Does it increase, decrease or stay approximately the same? If it changes, indicate by how much (give a number).
d) What happens to the reaction rate if the concentration of ethyl bromide is doubled and the concentration of potassium tert-butoxide is tripled? Does it increase, decrease or stay approximately the same? If it changes, indicate by how much (give a number).
e) What happens to the reaction rate if the temperature is raised?
4) (30 points) Solvolysis of Compound 1 ((E)-4-bromohex-2-ene) gives the four products shown. Propose a mechanism that shows how Product 1 and Product 4 are formed. Show curved arrows to illustrate the movement of electrons in each step. Draw all lone pairs and charges on all structures.
5) (15 points) Label each structure as Z, E or neither.
6) (15 points) Show how each compound might be synthesized by the SN2 displacement of an alkyl halide.
7) (15 points) Predict the major products of acid-catalyzed dehydration of the following alcohols.
8) (25 points) For each reaction, provide the major product(s). Clearly indicate the stereochemistry in each product. In the first 3 questions (a, b, c) give your answer in the form. of a Fisher projection Note: in parts a, b, c and d, the reaction mechanism is indicated.