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JEE Main levelOne or more correct optionsDifficulty 2 of 3o4103

Which of the following statements about the E1 mechanism of dehydrohalogenation are correct?

  1. AThe rate is and does not depend on the concentration of the base.
  2. BA carbocation intermediate is formed, so rearrangements by hydride or methyl shift can occur.
  3. CThe hydrogen and the leaving group must be anti-periplanar in the transition state of the rate-determining step.
  4. DPolar protic solvents favour the reaction.

Answer: A, B, D

In E1 the slow step is ionisation of the C-X bond, so the rate depends on the substrate only, and polar protic solvents stabilise the ionic intermediate. The carbocation may rearrange. The anti-periplanar requirement belongs to the concerted E2 mechanism, not to E1.
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