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JEE Advanced levelSingle correct optionDifficulty 3 of 3o3157

A single enantiomer of trans-1-chloro-2-(methylsulfanyl)cyclohexane is stirred in aqueous sodium hydrogen carbonate. The C-Cl bond is lost with anchimeric assistance by sulfur, and water opens the resulting episulfonium ion. The product, 2-(methylsulfanyl)cyclohexan-1-ol, is

  1. Athe cis-alcohol as a racemic mixture
  2. Bthe trans-alcohol as a racemic mixture
  3. Cthe cis-alcohol as a single enantiomer
  4. Dthe trans-alcohol as a single enantiomer, with retained configuration

Answer: B

Sulfur attacks the carbon bearing Cl from the back in the diaxial chair, giving a cis-fused episulfonium ion with a mirror plane through sulfur, so its two ring carbons are equivalent. Water opens the ring from the back at either carbon with equal probability. Each opening is an inversion, so both modes give trans product, and the two modes give opposite enantiomers, so the product is racemic trans-2-(methylsulfanyl)cyclohexan-1-ol.
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