Chapter 10.7, Problem BQ

Interpretation Introduction

Interpretation:

The intermediate in the Pinacol rearrangement that can be stabilized by resonance delocalization has to be identified.

Concept Introduction:

Pinacol rearrangement: For all glycols Pinacol rearrangement occurs. Unsymmetrical vicinal diols reveal that $\text{–OH}$ group that becomes protonated and leaves in the one that gives rise to more stable carbocation. Acid-catalyzed conversion of Pinacol to pinacolone followed by four step mechanism as follows,

Step 1: Add proton (protonation of Pinacol using acid catalyst).

Step 2: Break a bond to give a stable molecules or ions (formation of carbocation).

Step 3: 1, 2-shift (migration of substituent from $\text{α-}\text{to}\text{β-}$ carbon).

Step 4: deprotonation occurs (take a proton away).