Chapter 9, Problem 9.80P

Interpretation Introduction

Interpretation:

Among the given reactions, the reactions that proceed with carbocation rearrangement are to be identified.

Concept introduction:

The ${\text{S}}_{\text{N}}\text{1}$ and $\text{E1}$ reactions proceed with the formation of carbocation intermediate by elimination of the leaving group in the first step. This is the rate-determining step, thus the stability of the carbocation formed increases the rate of reaction. The electron donating groups (alkyl substituents) adjacent to the carbocation increase its stability. The order of stability of carbocation is ${\text{CH}}_{\text{3}}\text{}{\text{< 1}}^{\text{o}}{\text{ < 2}}^{\text{o}}{\text{ < 3}}^{\text{o}}$. The carbocation can be rearranged by $\text{1, 2-}$ hydride or $\text{1, 2-}$ methyl shift to form a more stable carbocation.

The ${\text{S}}_{\text{N}}\text{2}$ and $\text{E2}$ reactions are single step reactions that do not involve the formation of carbocation intermediate.

The leaving bonded to tertiary carbon proceeds with ${\text{S}}_{\text{N}}\text{1}$ or $\text{E1}$ reactions, and the leaving bonded to primary carbon proceeds with ${\text{S}}_{\text{N}}\text{2}$ or $\text{E2}$ reactions. The stronger nucleophile and aprotic solvent promotes ${\text{S}}_{\text{N}}\text{2}$ reaction.