Chapter 8, Problem 8.62P

Interpretation Introduction

Interpretation:

The complete, detailed mechanism for the reaction is to be drawn that shows the racemization at the alpha carbon.

Concept introduction:

An ${\text{S}}_{\text{N}}\text{1}$ reaction is a unimolecular nucleophilic substitution reaction and is a two-step reaction. In the first step, the leaving group breaks off, taking its bond pair with the carbon atom, thus forming a carbocation. In the second step, the incoming nucleophile attacks the carbocation, forming the product. Stereochemistry is important and applicable for an ${\text{S}}_{\text{N}}\text{1}$ reaction. The ${\text{S}}_{\text{N}}\text{1}$ reaction can be carried out in the presence of a strong base, in which the first step is the abstraction of proton. The alpha hydrogen atom is specifically abstracted by a proton as it is the most acidic proton in the reactant molecule.

The carbanion formed as an intermediate in the first step has a trigonal pyramidal geometry, but due to the delocalization of electrons, the carbon atom in the carbanion develops a planar geometry. Thus, the upcoming nucleophile can attack from either sides, which yields a mixture of both R and S enantiomers.