Chapter 8, Problem 8.70P

Interpretation Introduction

(a)

Interpretation:

A reasonable mechanism for the given pinacol rearrangement reaction is to be proposed.

Concept introduction:

The unimolecular elimination ($\text{E1}$) reaction consists of two steps. In first step, the leaving group leaves to form a carbocation intermediate; then ${\text{H}}^{\text{+}}$ is eliminated with the aid of a base to yield a double bond. A strong base is incompatible with acidic conditions. To avoid the formation of this species, the strong acids can protonate the oxygen prior to the heterolysis step. In the carbocation rearrangement, the carbocation gains significant stability from resonance delocalization of the charge.

Interpretation Introduction

(b)

Interpretation:

The reason for the carbocation rearrangement for the given reaction is to be explained.

Concept introduction:

In the carbocation rearrangement, the carbocation gains significant stability from resonance delocalization of the charge. Resonance can provide substantial charge stability.