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JEE Main levelSingle correct optionDifficulty 2 of 3g3266

A sample of the optically pure compound shown is stirred with aqueous NaOH. Which statement is correct?

  1. AIt slowly racemises because the stereocentre is an alpha carbon that loses its proton to give a planar achiral enolate.
  2. BIt keeps its configuration because the stereocentre C-H bond is never broken.
  3. CIt racemises only in acid, not in base.
  4. DIt is converted completely into the enantiomer by an process.

Answer: A

The compound shown is (R)-3-methylpentan-2-one, whose stereocentre carries a hydrogen and is directly bonded to the carbonyl carbon. Hydroxide removes this alpha proton to give a planar, achiral enolate, and reprotonation from either face gives both enantiomers, so the compound racemises. Acid also racemises it through the enol, so the last statement is wrong.
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