Test 2 Answers
Dr. Bachrach
CHEM 2319-2
3/19/2014

1) Provide the IUPAC name for the following compounds.

a)

(2Z)-7-ethyl-3,4-dimethyl-2,6-nonadiene

b)

(3S)-3-chloro-2,3-dimethylhexane

c)

(3E,5S)-5-bromo-3-ethyl-2-methyl-3-heptene

d)

(1R,2R)-1-ethyl-2-propylcyclobutane

2) Draw the Fischer projections of (3S,4R)-3-chloro-4-methylheptane.

3) For the reaction below, will the reaction proceed faster in ethanol (CH3CH2OH) or diethyl ether (CH3CH2OCH2CH3)? Explain your choice.

This is an SN2 reaction (its a primary alkyl halide!). The transition state will be:

The reactants have no charge, but are polar, and so both solvents will stabilize the reactants pretty much equivalently.

However, there is charge build up in the transition state: positive charge on the nitrogen and negative charge on the bromine. Now both solvents will stabilize the positive charge, but the protic solvent ethanol will also solvate the negative charge, much more so than with the aprotic solvent diethyl ether. So, ethanol will stabilize the TS more so than diethyl ether and lower the barrier.

The products are much more stabilized in ethanol than diethyl ether due to the full negative charge on bromide.

The reaction energy surfaces thus look like this:

The barrier is thus lower in ethanol than in diethyl ether and therefore the reaction is faster in ethanol.

4) For each pair of reactants, circle which one will react faster and identify the reaction mechanism.

a)

These reactions are definitely SN2 primary substrate in aprotic solvent. Therefore, the second reaction is faster because it has the better leaving group.

b)

These reactions are definitely SN1 tertiary or secondary substrate in protic solvent with a good leaving group. Therefore, the first reaction is faster because it is tertiary, forming the more stable tertiary cation, than the second reaction which forms a less stable secondary cation.

5) Predict the product(s) of the following reactions. Indicate the major product if there is more than one product obtained.

a)

SN1, so

b)

SN1, so

c)

SN1, so

d)

6) Provide< the MAJOR product only for the following reactions.

a)

 

b)

7) What is the relationship between each pair of compounds?

a)

(2R,4R)-2-bromo-4-chloropentane (2S,4R)-2-bromo-4-chloropentane

Their names indicate that they are diastereomers.

b)

(3E)-3-bromo-4,5-dimethyl-3-hexene (3Z)-3-bromo-4,5-dimethyl-3-hexene

Their names indicate that they are diastereomers.