Chapter 9.4, Problem 9.19P

Interpretation Introduction

Interpretation:

The best leaving group in the given compound has to be identified.

Concept Introduction:

The leaving group is the important one that also affects the mechanism by which the reaction proceeds.  The ${\text{S}}_{\text{N}}\text{1}$ and ${\text{S}}_{\text{N}}\text{2}$ mechanism are very much sensitive to the nature of leaving group.  If there is no leaving group in the substrate, then both the mechanism cannot operate.  In comparison, ${\text{S}}_{\text{N}}\text{1}$ mechanism is more sensitive than ${\text{S}}_{\text{N}}\text{2}$ mechanism, because the formation of carbocation by the loss of leaving group is the rate determining step in ${\text{S}}_{\text{N}}\text{1}$ mechanism.

The stability of the carbocation formed is more sensitive which means that the stability of the leaving groups is much more important.  Generally, the leaving groups are conjugate base of strong acids.  If the base is not stabilized, then it is a bad leaving group.  In few cases the bad leaving group (hydroxide) can be converted into good leaving group (protonated form) treating with strong acids.