JEE Main 2025 Jan 23 Shift 1, Chemistry Q12: Properties and Important Reactions of Aldehydes & Ketones

JEE Main2025Jan 23, Shift 1Chemistry

The major product of the following reaction is :

Solution

Propanal has two $α$ -hydrogens on its $α$ -carbon. Formaldehyde (HCHO) has none. With excess HCHO under base, propanal undergoes successive crossed aldol condensations: each $α$ -H is replaced by a $- C H_{2} O H$ group, exhausting both $α$ -Hs and giving a $- C (C H_{2} O H)_{2} - C H O$ intermediate.

Once no $α$ -H remains, the residual $- C H O$ undergoes a crossed Cannizzaro with another HCHO: HCHO acts as the reductant (becoming $H C O O^{-}$ ) and the substrate's $- C H O$ is reduced to $- C H_{2} O H$ .

Net result: $C H_{3} - C (C H_{2} O H)_{3}$ , i.e. the neopentyl-type triol shown in option (3).

This sequence is the classic Tollens (formose-type) reaction.

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JEE Main 2025 Jan 23 Shift 1, Chemistry Q12: Properties and Important Reactions of Aldehydes & Ketones

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