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JEE Advanced levelSingle correct optionDifficulty 3 of 3o4241

The compound shown is treated with sodium ethoxide in ethanol and compared with its epimer at the carbon bearing chlorine. Which pair describes its behaviour?

  1. AIt reacts more slowly and gives only the less substituted alkene (2-menthene)
  2. BIt reacts faster and gives only the less substituted alkene (2-menthene)
  3. CIt reacts faster and gives mainly the more substituted alkene (3-menthene)
  4. DIt reacts more slowly and gives mainly the more substituted alkene (3-menthene)

Answer: A

The compound is menthyl chloride, with chlorine equatorial in the stable chair. It must flip to the chair with chlorine, isopropyl and methyl all axial, which is unfavourable, so the reaction is slow. In that chair the C-2 hydrogen is equatorial (isopropyl is axial), so only the C-6 hydrogen is anti to chlorine and the less substituted 2-menthene is formed.
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