Chapter 9, Problem 9.6YT

Interpretation Introduction

Interpretation:

The leaving group in Table 9-4 that is the weakest base is to be identified from the ${\text{pK}}_{\text{a}}$ value of its conjugate acid. The ${\text{S}}_{\text{N}}\text{1}$ reaction rate for this leaving group is to be compared with the other bases.

Concept introduction:

A weak base is stable and is, therefore, a good leaving group. The ${\text{pK}}_{\text{a}}$ value of its conjugate acid is low, often negative. It has a strong conjugate acid and lower the ${\text{pK}}_{\text{a}}$ of the conjugate acid. Smaller the ${\text{pK}}_{\text{a}}$ value of weak base act as good leaving group.

The rate of an ${\text{S}}_{\text{N}}\text{1}$ reaction depends on the nature of the leaving group as the leaving group departs in the rate-determining step. The better the leaving group, the faster the rate of the corresponding ${\text{S}}_{\text{N}}\text{1}$ reaction.