Chapter 11, Problem 11.62SP

(a)

Interpretation Introduction

To determine: The mechanism of the given reaction that accounts for racemisation with excess inversion.

Interpretation: The mechanism of the given reaction that accounts for racemisation with excess inversion is to be stated.

Concept introduction: The reaction between $\text{butan-2-ol}$ and concentrated aqueous $\text{HBr}$ comprises two pathways first is through ${\text{S}}_{\text{N}}\text{2}$ reaction and second is through ${\text{S}}_{\text{N}}\text{1}$ reaction. When this reaction goes through ${\text{S}}_{\text{N}}\text{2}$ reaction, it gives more inversion (major product) than retention of configuration. When this reaction goes through ${\text{S}}_{\text{N}}\text{1}$ reaction, it gives only retention of configuration as mixture of equal amount of products (minor).

(b)

Interpretation Introduction

To determine: The mechanism of the given reaction that accounts for complete retention of configuration.

Interpretation: The mechanism of the given reaction that accounts for complete retention of configuration is to be stated.

Concept introduction: The reaction between $trans\text{-2-bromocyclopentanol}$ and concentrated aqueous $\text{HBr}$ comprises two pathways, first is through ${\text{S}}_{\text{N}}\text{2}$ reaction and second is through ${\text{S}}_{\text{N}}\text{1}$ reaction. Both the reactions yield complete retention of configuration products. However, in ${\text{S}}_{\text{N}}\text{2}$ reaction, it yields products in major amount.