JEE Main · 2025 · 23 Jan 2025 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

The major product of the following reaction is:

Answer: (C)

Solution

Propanal has two

α

-hydrogens on

C_{2}

, so with excess formaldehyde and base it undergoes two successive crossed aldol condensations, replacing both

α

-hydrogens with

- C H_{2} OH

groups:

C H_{3} C H_{2} CHO HCHO, O H^{-} C H_{3} - CH (C H_{2} OH) - CHO HCHO, O H^{-} C H_{3} - C (C H_{2} OH)_{2} - CHO

Once the

α

-carbon becomes quaternary, no

α

-hydrogen remains for further aldol addition. The resulting aldehyde, itself lacking an

α

-hydrogen, then undergoes a crossed Cannizzaro reaction with excess formaldehyde: the aldehyde carbon is reduced to a

- C H_{2} OH

group while formaldehyde is oxidised to formate.

C H_{3} - C (C H_{2} OH)_{2} - CHO + HCHO O H^{-} C H_{3} - C (C H_{2} OH)_{3} + HCO O^{-}

The major product is 2-methyl-2-(hydroxymethyl)propane-1,3-diol,

C H_{3} - C (C H_{2} OH)_{3}

JEE Main · 2025 · 23 Jan 2025 · Shift 1 · Single correct option