Chemistry 331 - Winter 1996
Elements of Organic Chemistry I

Professor Carl C. Wamser

EXAM 2 - Answer Key
February 27, 1996

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1. (15 points) Write complete names for each of the following, including designation of stereochemistry.

a)
(S)-5-bromo-5-chloro-2-heptyne

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b)
(1S,3S)-1,3-dichloro-1-methylcyclohexane

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c)
(R)-2,3,5-trimethyl-1,3-cyclohexadiene

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2. (12 points) Complete each of the following reactions by adding the missing part: either the necessary reagents and conditions, or the final major product.

a)

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b)

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c)

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d)

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3. (12 points) Circle all of the structures that correspond to (R)-2-chlorobutane.

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4. (5 points) Identify with an asterisk (*) all of the stereogenic centers in the structure shown below (R & S designations not necessary here).

Aspartame, an artificial sweetener (Equal)

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5. (10 points) Identify as R or S each of the two stereogenic centers in threonine, shown below. Add the missing substituents to the structure on the right.

threonine, a naturally occurring amino acid

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6. (14 points) Shown below are three alkene isomers labeled X, Y, and Z. Also shown below are four alkyl bromide isomers labeled A, B, C, and D.



Apply Markovnikov's Rule to predict the major product from addition of HBr to each of the alkenes.

X + HBr ---> B
Y + HBr ---> C
Z + HBr ---> C

Apply Zaitsev's Rule to predict the major product of elimination from each of the alkyl bromides.

A + KOH ---> X
B + KOH ---> Y
C + KOH ---> Y
D + KOH ---> Z

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7. (12 points) Complete the following reaction scheme by adding the missing parts:

8. (20 points) Styrene, shown below, might react with a strong electrophile in two distinct ways:

a) The electrophile might add to the aromatic ring. Show the intermediate that would result from attack of E+ at the para position, including all resonance forms.


b) The electrophile might add to the double bond. Show the intermediate that would result from addition of E+ according to Markovnikov's Rule, including all resonance forms.


c) Which do you think actually occurs? Explain your answer with a justification of the relative likelihood of each possibility.

Addition to the double bond is more favorable than addition to the aromatic ring. The intermediate carbocation is more stable, relative to the starting compound, because the aromatic ring is kept intact. In general, only very strong electrophiles add to an aromatic ring, but normal electrophiles can add to a double bond.