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JEE Advanced levelSingle correct optionDifficulty 3 of 3hx219

A single enantiomer of cis-1-bromo-3-methylcyclohexane is treated with in DMF (pure SN2 at C-1). The product 3-methylcyclohexane-1-thiol is

  1. Athe trans isomer, formed as a racemic mixture
  2. Bthe cis isomer, formed as a single enantiomer
  3. Cthe cis isomer, formed as a meso compound
  4. Dthe trans isomer, formed as a single enantiomer (optically active)

Answer: D

SN2 inverts only C-1, so cis becomes trans. Only one of the two stereocentres is changed, and the substrate is a single enantiomer, so the product is also a single enantiomer. trans-1,3-Disubstituted cyclohexanes are chiral (no mirror plane), so there is no meso form.
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