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JEE Main levelOne or more correct optionsDifficulty 2 of 3o3141

Select the correct statement(s) about neighbouring group participation (NGP) in nucleophilic substitution.

  1. AThe participating group must carry a lone pair or electrons to act as an internal nucleophile.
  2. BThe rate of an NGP reaction depends strongly on the concentration of the external nucleophile.
  3. CNGP usually gives a faster reaction than the analogue lacking the participating group.
  4. DWhen the first and second steps are both SN2 displacements at the same carbon, the net result at that carbon is retention.

Answer: A, C, D

NGP involves an intramolecular rate-determining step that is faster than the intermolecular alternative, giving rate acceleration. Two inversions give retention. The internal nucleophile must have a donor lone pair or bond. The external nucleophile enters after the rate-determining step, so the rate does not depend on its concentration.
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