EXAM 3
CHEMISTRY 220
Friday, November 7, 1997
NAME (print): ___________________________________________________
TA:_____________________ Day:_________________ Time:__________
Important points are in bold.
Take a few moments to look over the exam. Do the questions first with which you feel
most comfortable. Answer each question on the exam paper.
Do all preliminary drawing or computations on the work sheets at the end of the exam.
There is a Periodic Table of the Elements at the end of the exam.
The exam is 55 minutes.
STOP writing when you are asked to do so.
REMEMBER: Neatness is to your advantage.
1. (20 pts) ______
2. (20 pts) ______
3. (20 pts) ______
4. (20 pts) ______
5. (20 pts) ______
________________________________
Total (100 pts)
1. (4 x 5 pts = 20 pts) Provide an answer and brief rationale for each of the following
questions or statements.
a) Of the two primary halides, n-butyl bromide and isobutyl bromide, which one gives
the largest ratio of E2/SN2 products when treated with CH3ONa in CH3OH?
b) Why is the conversion of 2-butanol to 2-bromobutane with HBr an effective
synthetic reaction while the conversion of 2-hexanol to 2-bromohexane with HBr is not
an effective synthetic reaction?
c) Oxidation of hydroxyaldehyde 1 with pyridinium chlorochromate (PCC) does not
give the expected dialdehyde but rather the cyclic ester 2.
d) The better method for the preparation of cyclohexyl ethyl ether by an SN2
mechanism.
2. (20 pts) (2R, 5S)-5-Bromo-2-hexanol A reacts with PBr3 to form a dibromide B. B
forms 2,5-dimethyltetrahydrothiophene C (C6H12S) when treated with H2S in the
presence of aqueous KOH. Structure 1 is thiophene.
a) (7 pts) What is the structure of B and what is its mechanism of formation? Provide
configurations.
b) (7 pts) What is the structure C and what is its mechanism of formation? Provide
configurations.
c) (6 pts) Is C optically active? Explain briefly.
3. (4 x 5pts = 20 pts) Provide reagents for accomplishing each of the following
reactions. More than one step may be involved. Explain briefly.
4. (4 x 5 pts = 20 pts) For each of the following substitution reactions, predict and
explain briefly which ones will occur as described and which ones will not.
a) (R)-2-bromobutane + excess LiI ----> (S)-2-iodobutane
b) CH3CH2CH2OH + NH2- ----> CH3CH2CH2NH2 + OH-
c) CH3CH2CN + OH- ----> CH3CH2OH + CN-
d) t-butyl bromide + NaOCH3 ----> t-butyl methyl ether + NaBr
5. (4 x 5 pts = 20 pts) In each of the following pairs of reactions, predict and explain
briefly which one is the faster reaction.
