Chemistry - Halogen Derivative Question with Solution | TestHub

Question Explanation: The question asks how many of the given elimination reactions produce the Hofmann alkene (less substituted alkene) as the major product.

Concept: This question is based on Elimination Reactions, Hofmann Rule, E2 Mechanism, E1 Mechanism, and Leaving Group Effect.

Solution:

(a) Tertiary butoxide ion is a bulky base, which prefers abstracting the least hindered $\beta$-H, leading to the Hofmann product.

(b) Quaternary ammonium salt on heating undergoes Hofmann elimination, resulting in the less substituted alkene as the major product.

(c) Alkyl fluoride with alcoholic KOH: F⁻ is a poor leaving group, so the reaction follows an E2 mechanism with Hofmann orientation, making the Hofmann product major.

(d) Dehydration with conc. H₃PO₄ proceeds via an E1 mechanism, giving the Saytzeff product, not Hofmann.

(e) Ester on heating undergoes Eᵢ / pyrolytic elimination, favoring the Hofmann alkene.

Thus, reactions (a), (b), (c), and (e) give the Hofmann product as the major product.