Question

Does Hoffman's Rule apply to E1 Rxns too or to just E2 rxns

Answer 1

Hoffman rule: According to this rule, beta hydrogen is abstracted by base from the most unhindered (i.e. least substituted) position and least substituted alkene is obtained as a product.

Hoffman rule mostly applies to E2 reactions as in E2 mechanism, a strong and bulky base is used to abstract the beta hydrogen as the mechanism is concerted one. But due to the steric hindrance , bulky base abstracts the hydrogen from the outer surface and give least substituted alkene as product.

e.g.

while E1 elimination takes place through the carbocation intermediate and in this mechanism weak base can also do deprotonation to give alkene.