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JEE Main levelSingle correct optionDifficulty 2 of 3o4009

A tertiary alkyl bromide reacts in ethanol with no added base. Replacing every beta-hydrogen by deuterium changes the overall rate of consumption of the bromide by only a few per cent. This observation shows that

  1. Athe reaction is a concerted anti-elimination
  2. Ba carbanion is formed in the slow step
  3. Cthe C-H bond is broken in the rate-determining step, as expected for E2
  4. Dthe C-H bond is not broken in the rate-determining step, as expected for E1

Answer: D

A large primary isotope effect needs the C-H bond to break in the rate-determining step. A near-unit effect means C-H cleavage occurs after the slow step, as in E1 where the slow step is ionisation, and the proton is lost from the carbocation.
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