Question

The following 1, 2 diol undergoes the pinacol rearrangement. Predict the product.

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

Vicinal diols in acidic conditions $\left(H^{+}/H_{2}S{O}_4\right)$ undergoes pinacol-pinacolone rearrangement.
Mechanism of pinacol-pinacolone:
In first step, the protonation of alcohol occurs to form a stable carbocation. Protonation occurs to the particular $OH$ group which form a stable carbocation.
In step 2, rearrangement of carbocation occurs. Here, carbocation undergo 1, 2 H-shift to form a resonance stabilised oxonium ion.
In step 3, deprotonation occurs in oxonium ion to a pinacolone.