Chapter 21, Problem 21.43P

Interpretation Introduction

(a)

Interpretation:

The complete, detailed mechanism for the given reaction is to be drawn. Why ${\text{R}}^{-}$ can act as a leaving group in this reaction is to be explained.

Concept introduction:

The carbon atom in a carbonyl group is relatively electron-poor as it is bonded to a highly electronegative oxygen. A nucleophile can, therefore, add to this carbon, forming a tetrahedral intermediate. If a suitable leaving group is present on the initial carbonyl carbon, it will be eliminated, reforming the carbonyl group to give the product. If the nucleophile added in the first step is neutral and has a proton attached to the electron-rich atom, a proton transfer step occurs before the elimination step.

In case the carbonyl carbon of the substrate is a part of a highly strained ring, the elimination step can lead to ring opening, with one of the carbons adjacent to the carbonyl carbon breaking off as $-{\text{CH}}_{\text{2}}{}^{-}$.

Interpretation Introduction

(b)

Interpretation:

The synthesis of an ester using only the reaction from part (a) is to be proposed.

Concept introduction:

Treatment of a highly strained cyclic ketone with a nucleophile results in a nucleophilic addition-elimination reaction that leads to ring opening. Depending on the nucleophile used, the end product may be a carboxylate ion, an ester, or an amide.