Chapter 13, Problem 13.14P

Interpretation Introduction

Interpretation:

How the nucleophilic substitution reaction corresponding to the transform shown can be carried out in a protic solvent is to be shown.

Concept introduction:

An ${\text{S}}_{\text{N}}2$ reaction is a single-step reaction in which the nucleophile attacks the electrophilic carbon before the bond between the carbon and the leaving group is broken. This requires the nucleophile to approach the carbon atom from a direction opposite to the leaving group. If the reaction center is a chiral carbon, this leads to a single product with inversion of the configuration.

An ${\text{S}}_{\text{N}}1$ is a two-step reaction that involves the formation of a planar carbocation intermediate. If the carbon at the reaction center is a chiral carbon in the product, this leads to the formation of a mixture of enantiomers.

Therefore, the stereochemistry of the reaction center can dictate the choice of the reaction mechanism.

Polar protic solvents tend to disfavor ${\text{S}}_{\text{N}}2$ reactions. However, if a protic solvent is needed, it must be one that will not compete with the nucleophile. If the nucleophile is anionic, this means the conjugate acid of the nucleophile is a good choice for the solvent.