JEE Main 2025 Apr 3 Shift 2, Chemistry Q7: Properties and Important Reactions of Aldehydes & Ketones

The substrate is phenylglyoxal, Ph$-$CO$-$CHO, a 1,2-dicarbonyl compound bearing no $\alpha$-hydrogen on either carbonyl carbon. Under strong base (KOH), such systems undergo an intramolecular Cannizzaro-type 1,2-hydride shift.

Step 1: OH${}^{-}$ adds to the more electrophilic aldehyde carbon, giving a tetrahedral alkoxide.

Step 2: The hydride migrates from the former aldehyde carbon to the adjacent ketone carbon (rate-determining intramolecular shift).

Step 3: Proton transfers produce the $\alpha$-hydroxy carboxylate, i.e. the potassium salt of mandelic acid: Ph$-$CH(OH)$-$COO${}^{-}$K${}^{+}$.

$\therefore$ Option (2) is the major product.