MolSynapsequestion bank
MolSynapse / Question bank / Organic Reaction Mechanisms IV: Elimination / E1cB mechanism
JEE Main levelSingle correct optionDifficulty 2 of 3o4135

A substrate that undergoes base-induced elimination is recovered partway through the reaction from . The recovered unreacted material has deuterium at the beta carbon, and exchange is faster than product formation. This indicates that

  1. Athe reaction is a concerted E2 process
  2. Ba carbocation intermediate is formed
  3. Ca carbanion forms reversibly and its return to the reactant is faster than loss of the leaving group
  4. Dthe reaction is E1 with rate-determining ionisation

Answer: C

Incorporation of D at the beta carbon in unreacted substrate means the beta C-H bond is broken and reformed, so a carbanion forms reversibly. Exchange outpacing elimination means the carbanion re-protonates faster than it expels the leaving group, which is E1cB with reversible carbanion formation.
Practice Organic Reaction Mechanisms IV: Elimination More on E1cB mechanism
Previous questionNext question

More questions on E1cB mechanism