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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3hx231

The optically pure benzylic bromide shown is left in aqueous acetone with no added strong nucleophile and reacts by an (idealised) SN1 mechanism to give the alcohol. Select all correct statements.

  1. AThe rate depends on the concentration of the bromide only.
  2. BThe intermediate is a planar benzylic carbocation stabilised by resonance.
  3. CThe alcohol is formed with complete inversion of configuration.
  4. DThe alcohol obtained is optically active and entirely of the same configuration as the reactant.

Answer: A, B

The benzylic C-Br bond ionises (slow step) to a resonance-stabilised planar carbocation, so the rate depends only on the bromide concentration. Water attacks either face, so the alcohol is formed as a racemate; neither complete inversion nor complete retention results.
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