In the NaOH-catalysed condensation of acetophenone with benzaldehyde, the aldol C6H5COCH2CH(OH)C6H5 loses water to give chalcone. The species from which hydroxide leaves and the configuration of the main product are

a benzylic carbocation; (Z)-chalcone

a benzylic carbocation; (E)-chalcone

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JEE Advanced levelSingle correct optionDifficulty 3 of 3o4049

In the NaOH-catalysed condensation of acetophenone with benzaldehyde, the aldol $C X_{6} H X_{5} COCH X_{2} CH (OH) C X_{6} H X_{5}$ loses water to give chalcone. The species from which hydroxide leaves and the configuration of the main product are

Aa benzylic carbocation; (Z)-chalcone
Ban enolate; (E)-chalcone
Ca benzylic carbocation; (E)-chalcone
Dan enolate; (Z)-chalcone

Answer: B

The base removes an alpha-hydrogen (acidic, next to C=O) to give the enolate

C X_{6} H X_{5} C (O X^{-}) = CH - CH (OH) C X_{6} H X_{5}

, which expels

OH X^{-}

(E1cB). Rotation in the carbanion before expulsion lets the two bulky groups stay trans, so the thermodynamically more stable (E)-1,3-diphenylprop-2-en-1-one is the main product.

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In the NaOH-catalysed condensation of acetophenone with benzaldehyde, the aldol CX6​HX5​COCHX2​CH(OH)CX6​HX5​ loses water to give chalcone. The species from which hydroxide leaves and the configuration of the main product are

Answer: B

More questions on E1cB mechanism

In the NaOH-catalysed condensation of acetophenone with benzaldehyde, the aldol $C X_{6} H X_{5} COCH X_{2} CH (OH) C X_{6} H X_{5}$ loses water to give chalcone. The species from which hydroxide leaves and the configuration of the main product are