JEE Main 2026 Apr 6 Shift 2, Chemistry Q19: Properties and Important Reactions of Aldehydes & Ketones

JEE Main2026Apr 6, Shift 2Chemistry

Consider the following reactions. Total number of electrons in the $π$ bonds and lone pair of electrons in the product $(X)$ is:

Solution

Identify $X$ .

(i) HI / red P / $Δ$ on glucose reduces all C–OH and CHO into a saturated hydrocarbon: $n$ -hexane.

(ii) V $_{2}$ O $_{5}$ at 773 K and 10–20 atm aromatises $n$ -hexane to benzene.

(iii) Friedel-Crafts acylation with PhCOCl/AlCl $_{3}$ gives benzophenone, Ph–CO–Ph.

Count $π$ + lone-pair electrons in benzophenone.

$π$ electrons: each benzene ring contributes 6 $π$ electrons ( $2 \times 6 = 12$ ); the C=O contributes 2. Total $π$ = 14.

Lone pairs on oxygen: 2 lone pairs = 4 electrons.

Total = $14 + 4 = 18$ .

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