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JEE Advanced levelSingle correct optionDifficulty 3 of 3o4143

Benzaldehyde and acetophenone react with aqueous to give chalcone. In the dehydration step of the intermediate , the species that loses and the major product are

  1. Athe carbocation ; (E)-1,3-diphenylprop-2-en-1-one
  2. Bthe enolate ; (E)-1,3-diphenylprop-2-en-1-one
  3. Cthe enolate ; (Z)-1,3-diphenylprop-2-en-1-one
  4. Dthe alkoxide ; (E)-1,3-diphenylprop-2-en-1-one

Answer: B

Hydroxide removes the alpha-H of the ketone to give the enolate, which expels from the adjacent carbon (E1cB). The alpha-H is the acidic one. The E isomer of the conjugated product is more stable (less steric clash between the phenyl groups) and forms preferentially.
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