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JEE Main levelSingle correct optionDifficulty 2 of 3o3252

The trans-disubstituted sulfonate shown is heated in acetic acid (acetolysis) and compared with its cis isomer. Which statement is correct?

  1. AThe trans isomer reacts much faster and gives trans diacetate with retention of configuration
  2. BThe cis isomer reacts faster because the groups are close
  3. CBoth react at equal rates because the leaving group is the same
  4. DThe trans isomer reacts faster and gives the cis diacetate with inversion

Answer: A

The compound is trans-2-acetoxycyclohexyl methanesulfonate (diol-type pattern: [C@H]...[C@@H] is the trans one, RDKit labels S,S). The acetoxy carbonyl oxygen can attack the carbon bearing OMs from the back side only when the two groups are trans (diaxial), forming a cyclic acetoxonium ion. This anchimeric assistance makes the trans isomer react far faster than the cis isomer, and opening of the ion by acetate leads to the trans diacetate with net retention.
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