Chapter 8, Problem 8.58P

Interpretation Introduction

Interpretation:

A complete, detailed mechanism is to be drawn that accounts for the given product. It is also to be explained why the carbocation rearrangement is favorable.

Concept introduction:

An ${\text{S}}_{\text{N}}\text{1}$ reaction is a two-step reaction. In the first step, the leaving group breaks off, taking its bond pair with the carbon atom, thus forming a carbocation. In the second step, the incoming nucleophile attacks the carbocation, forming the product.

The carbocation formed in the first step can rearrange to another one as a result of resonance (delocalization) if it is adjacent to a double or triple bond. A $\text{1, 2-hydride}$ shift or a $\text{1, 2-methyl}$ shift is also a possibility if it leads to the formation of a more stable carbocation. A rearrangement like this can lead to the formation of two constitutional isomers. The difference in the carbon skeleton points out that the rearrangement could have taken place. The more stable carbocation is favored over the ones that are not stable.