Question

The elimination takes place by which mechanism?

• A. $E_1$
• B. $E_2$
• C. $E_i$
• D. $E_{1}cB$

Answer 1

The correct option is D $E_{1}cB$

$E_{1}cB$ takes place in a basic medium where the H atom that can be removed should be relatively acidic. A presence of a poor leaving group is also necessary. Here $\alpha -H$ is acidic and OH is a very poor leaving group. In a basic medium, the reaction can go only through $E_{1}cB$.
Progress of the reaction is as follows:
(a) Base abstracts $\alpha -H$:

(The generated anion is resonance stabilised)

(b) Elimination of hydroxyl group: