Q3. 3 explain with a detailed mechanism, why a b-hydroxyketone is not isolated as the final product in the base catalysed condensation of acetophenone and benzaldehyde. (5)

A conjugated system is most stable than a β-hidroxyketone.

Explanation:

The mechanism is the chalcone synthesis. (Look picture).

The first step consist in the formation of enol from acetophenone (That occurs because hydrogens of α-carbon are acid).

Then, this α-carbon acts as nucleophile and carbon of aldehyde is electrophile.β-hidroxyketone is formed by equilibrium with water.

The last step is the formation of chalcone. That occurs because the formed product is very stable by conjugation.

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