JEE Main 2026 Apr 8 Shift 2, Chemistry Q22: Properties and Important Reactions of Aldehydes & Ketones

JEE Main2026Apr 8, Shift 2Chemistry

'x' is the product which is obtained from benzene by reacting it with carbon monoxide and hydrogen chloride in the presence of cuprous chloride. 'y' is the major product obtained from the benzene by reacting it with ethanoyl chloride in the presence of anhydrous AlCl $_{3}$ . Product (major) obtained by heating x and y in the presence of alkali is z. Total number of $π$ (pi) electrons in z is _______.

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Solution

Identify x. Benzene + CO + HCl over Cu $_{2}$ Cl $_{2}$ /AlCl $_{3}$ is the Gattermann–Koch reaction, which installs a $-$ CHO group on the ring. So x = benzaldehyde, C $_{6}$ H $_{5}$ CHO.

Identify y. Benzene + CH $_{3}$ COCl/anh. AlCl $_{3}$ is Friedel–Crafts acylation, giving y = acetophenone, C $_{6}$ H $_{5}$ COCH $_{3}$ .

Identify z. Mixing benzaldehyde and acetophenone in aqueous NaOH and heating is a Claisen–Schmidt (crossed aldol) condensation. The $α$ -H of acetophenone is removed, the resulting enolate attacks benzaldehyde's carbonyl, and dehydration gives the $α, β$ -unsaturated ketone (E)-chalcone: C $_{6}$ H $_{5}$ –CH=CH–C(=O)–C $_{6}$ H $_{5}$ .

Count $π$ electrons in z.

Each phenyl ring contributes $6$ $π$ electrons: $2 \times 6 = 12$ .

The CH=CH double bond contributes $2$ .

The C=O contributes $2$ .

Total: $12 + 2 + 2 = 16$ $π$ electrons.

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JEE Main 2026 Apr 8 Shift 2, Chemistry Q22: Properties and Important Reactions of Aldehydes & Ketones

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