Chapter 20, Problem 20.31P

Interpretation Introduction

(a)

Interpretation:

The major organic product of the given reaction is to be predicted, and the mechanism for the given reaction is to be drawn.

Concept introduction:

In a transesterification reaction, one ester is converted into another. The mechanism for the transesterification reaction involves a nucleophile and a carboxylic acid derivative. This reaction is known as a nucleophilic addition-elimination reaction, which takes place in two steps. In the first step, the nucleophile adds to the electron-poor carbon in the carboxylic acid derivative. A tetrahedral intermediate is created. In the next step, the $\text{C}=\text{O}$ bond is regenerated, and the leaving group (alkoxide ion) leaves. Overall, nucleophilic elimination results in substitution at the carbonyl carbon that is part of an acyl group. Cyclic esters tend to undergo ring-opening transesterification reactions.

Interpretation Introduction

(b)

Interpretation:

The major organic product of the given reaction is to be predicted, and the mechanism for the given reaction is to be drawn.

Concept introduction:

In a saponification reaction, an ester reacts with ${\text{HO}}^{-}$ to produce an initial carboxylic acid that is rapidly and irreversibly deprotonated under the basic conditions. This is an example of a nucleophilic addition-elimination reaction. In the first step, the nucleophile adds to the electron-poor carbon in the carboxylic acid derivative. A tetrahedral intermediate is created. In the next step, the $\text{C}=\text{O}$ bond is regenerated, and the leaving group (alkoxide ion) leaves. Two back to back proton transfer reactions take place to yield an original carboxylic acid.