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JEE Advanced levelSingle correct optionDifficulty 3 of 3o3156

A single enantiomer of trans-2-acetoxycyclohexyl tosylate is heated with potassium acetate in acetic acid. The reaction proceeds by participation of the neighbouring acetoxy group through a cis-fused cyclic acetoxonium ion, which is opened by acetate. The product, cyclohexane-1,2-diyl diacetate, is

  1. Ameso cis-diacetate
  2. Boptically pure trans-diacetate with inverted configuration at both carbons
  3. Coptically pure trans-diacetate with retained configuration at both carbons
  4. Dracemic trans-diacetate

Answer: D

The acetoxy oxygen attacks the C-OTs carbon from the back, giving a cis-fused dioxolanylium (acetoxonium) ion. This ion has a mirror plane, so its two ring carbons are equivalent enantiotopic sites. Acetate attacks either carbon from the back with equal probability; attack at the original carbon gives retention, attack at the other gives the mirror-image diacetate. The product is the racemic trans-diacetate ((1R,2R) and (1S,2S) in equal amounts).
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