Question

Predict the product "A".

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

Vicinal diols in acidic conditions $\left(H^{+}/H_{2}S{O}_4\right)$ undergoes pinacol-pinacolone rearrangemt.
Mechanism of pinacol-pinacolone:
In first step, the protonation of alcohol occurs to form a stable carbocation. Here, both $OH$ groups are identical so protonation of any one $OH$ will give the same carbocation.
In step 2, rearrangement of carbocation occurs. Here, carbocation undergo 1, 2 alkyl shift to form a resonance stabilised oxonium ion.
In step 3, deprotonation occurs in oxonium ion to a pinacolone.