Chapter 9, Problem 9.42P

Interpretation Introduction

Interpretation:

Whether the given reaction occurs by an ${\text{S}}_{\text{N}}\text{2}$, ${\text{S}}_{\text{N}}\text{1}$, $\text{E2}$, or $\text{E1}$ mechanism is to be determined and a complete, detailed mechanism that accounts for the formation of the two products is to be drawn.

Concept introduction:

${\text{S}}_{\text{N}}\text{2}$ and ${\text{S}}_{\text{N}}\text{1}$ are nucleophilic substitution mechanisms. The first is a single-step bimolecular reaction while the second is a two-step unimolecular reaction.

An $\text{E1}$ reaction is a two-step, unimolecular elimination reaction. The reaction involves the formation of a carbocation intermediate in the first, rate-determining step. The carbocation may be subject to a rearrangement if it leads to a more stable carbocation. In the second step, a base abstracts a proton from an adjacent carbon to form the product. Because of the possibility of carbocation rearrangement, the reaction often yields a mixture of constitutional isomers.

An E2 elimination reaction involves both the substrate and the base in a single concerted step. In most cases, this results in a single product.