Exam 3 Answer Key

1. (15 points) Write complete names for each of the following.

a)

b)

c)

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2. (15 points) Write accurate structures for the following:

a) two diastereomers of 2,3-dichlorobutane

b) two enantiomers of 2,3-dichlorobutane

c) ozonolysis products from 2-pentyne

d) (R,R)-1,2-dimethylcyclopentane

e) the transition state for an SN2 reaction of I- with isobutyl bromide

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3. (15 points) Arrange each of the following in order with respect to the property indicated.
Write “MOST” under the compound with the highest value and “LEAST” under the compound with the lowest value.

a) nucleophilicity

b) reactivity in an SN2 mechanism

c) reactivity towards methyl iodide

d) acidity

e) ratio of substitution/elimination using NaOEt in EtOH

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4. (15 points) Complete the following reactions by indicating the major product expected. Show stereochemistry if it is specific.
If the reaction can be described as SN1, SN2, E1, or E2, indicate that.

a)

b)

c)

d)

e)

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5. (15 points) Complete the following structures so as to show both enantiomers of trans-1,3-dichlorocyclohexane in both of their chair conformations. Place the Cl substituents on the positions marked with the dots.

 

Identify each stereocenter as R or S on EVERY structure.

Identify which conformation is the more stable one for each enantiomer.

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6. (10 points) Preparation of 2,3-dibromobutane from 2-butyne can be done by addition of one equivalent of Br2 and one equivalent of H2.

Show the addition of Br2 (anti) followed by the addition of H2 (syn), specifically illustrating the stereoisomers that would be formed at each stage.

Does it matter whether the order of addition was reversed?

Illustrate the process for a syn addition of one equivalent of H2 followed by an anti addition of Br2.

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7. (15 points) Show how you could prepare butane, starting from acetylene as your ONLY source of carbon.

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