Chapter 8, Problem 8.27P

Interpretation Introduction

Interpretation:

Why the given ${\text{S}}_{\text{N}}\text{2}$ step is unreasonable is to be explained and an alternate, more reasonable mechanism is to be provided.

Concept introduction:

Mechanism of a reaction may be made up of a number of elementary steps. An elementary step generally involves only one or two reactant molecules. An elementary step involving three or more molecules is extremely rare because it would involve a collision of three (or more) molecules at exactly the same moment, and also in a particular orientation. This is extremely rare, and therefore, an unreasonable step.

The species involved in a proposed elementary step should be compatible with the reaction conditions, particularly pH.