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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3o3162

trans-2-Acetoxycyclohexyl tosylate and cis-2-acetoxycyclohexyl tosylate solvolyse in acetic acid at very different rates. Select the correct statement(s).

  1. AParticipation by the acetoxy oxygen requires an anti-periplanar (diaxial) relationship between the acetoxy oxygen and the C-OTs bond.
  2. BThe trans isomer can reach the required geometry by ring flipping to the diaxial chair, although the diequatorial chair is more stable.
  3. CIn the cis isomer the chair with both substituents equatorial allows participation.
  4. DThe cis isomer reacts faster because the two substituents are closer.

Answer: A, B

A backside attack by the neighbouring group requires it to be anti to the leaving group, which on a cyclohexane ring means both groups axial. This is accessible only for the trans isomer. In the cis isomer one group is always equatorial and the other axial, so the participation is geometrically impossible, and the cis isomer reacts much more slowly.
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