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In which of the following reactions is the product formed in accordance with Hofmann's rule (elimination preferentially gives the less substituted alkene)? (A) CH3CH2CH(Br)CH3 treated with alcoholic KOH under heat (B) CH3CH2CH(Br)CH3 treated with CH3ONa in CH3OH under heat (C) CH3CH2CH(CH3)N+(CH3)3 treated with OH- under heat (D) CH3CH2CH(S+(CH3)2)CH3 treated with OH- under heat
- Option A only
- Option B only
- Option C only
- Options C and D only
Correct answer: Options C and D only
Solution
Reactions A and B involve a secondary alkyl bromide; with alcoholic KOH (A) or sodium methoxide (B), Zaitsev elimination is favoured giving the more substituted but-2-ene. Reactions C and D involve quaternary ammonium and sulfonium salts respectively, where the bulky leaving group forces attack at the less hindered beta carbon, yielding the Hofmann product (less substituted alkene).
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