7. Substitution Reactions

What substitution products are obtained when each of the following compounds is added to a solution of sodium acetate in acetic acid?

a. 2-chloro-2-methyl-3-hexene

b. 3-bromo-1-methylcyclohexene

Draw the substitution products for each of the following S_N2 reactions. If the ­products can exist as stereoisomers, show which stereoisomers are formed:

a. (3S,4S)-3-bromo-4-methylhexane + CH₃O^-

b. (3S,4R)-3-bromo-4-methylhexane + CH₃O^-

Draw the substitution products for each of the following S_N2 reactions. If the ­products can exist as stereoisomers, show which stereoisomers are formed:

c. (3R,4R)-3-bromo-4-methylhexane + CH₃O^-

d. (3R,4S)-3-bromo-4-methylhexane + CH₃O^-

Propose a mechanism for the following reaction.

Draw the substitution and elimination products.

a.

b.

What nucleophiles would form the following compounds as a result of reacting with 1-iodobutane?

a.

b.

What nucleophiles would form the following compounds as a result of reacting with 1-iodobutane?

e.

f.

Aldolase shows no activity if it is incubated with iodoacetic acid before fructose-1,6-bisphosphate is added to the reaction mixture. What causes this loss of activity?

Predict the major products of the following substitutions.

a.

Predict the major products of the following substitutions.

f.

Chlorocyclohexane reacts with sodium cyanide (NaCN) in ethanol to give cyanocyclohexane. The rate of formation of cyanocyclohexane increases when a small amount of sodium iodide is added to the solution. Explain this acceleration in the rate.

Draw perspective structures or Fischer projections for the substitution products of the following reactions.

(b)

a. Optically active 2-bromobutane undergoes racemization on treatment with a solution of KBr. Give a mechanism for this racemization.

b. In contrast, optically active butan-2-ol does not racemize on treatment with a solution of KOH. Explain why a ­reaction like that in part (a) does not occur.

For each reaction, give the expected substitution product, and predict whether the ­mechanism will be predominantly first order (SN1) or second order (SN2).

c. 1-iodo-1-methylcyclohexane + ethanol

The following reaction takes place under second-order conditions (strong nucleophile), yet the structure of the product shows rearrangement. Also, the rate of this reaction is several thousand times faster than the rate of substitution of ­hydroxide ion on 2-chlorobutane under similar conditions. Propose a mechanism to explain the enhanced rate and ­rearrangement observed in this unusual reaction. (“Et” is the abbreviation for ethyl.)