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JEE Main levelSingle correct optionDifficulty 2 of 3o4024

2-Phenylethyl bromide and its analogue react with in ethanol at the same temperature, and the first reacts about 7 times faster. This result shows that

  1. Athe slow step is ionisation to a primary carbocation
  2. Bthe beta C-H bond is cleaved in the rate-determining step, consistent with E2
  3. Cthe beta C-H bond is not broken in the slow step, so the reaction is E1
  4. Dthe reaction is SN2 at the carbon bearing bromine

Answer: B

A primary isotope effect of about 7 is large; it means that the C-H bond to the beta-carbon is being broken in the rate-determining step, as it is in the single-step E2 transition state.
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