JEE Main 2026 Jan 24 Shift 2, Chemistry Q2: Properties and Important Reactions of Aldehydes & Ketones

Acidic hydrolysis of the unsaturated ether cleaves the $\text{C}-\text{O}-\text{C}$ linkage and tautomerizes the resulting enols to carbonyls:

$\text{P}={\text{CH}}_3{\text{CH}}_2\text{CHO}$ (propanal, an aldehyde)

$\text{Q}={\text{CH}}_3{\text{COCH}}_3$ (acetone, a ketone)

Fehling's solution oxidizes aliphatic aldehydes to give a red-brown ${\text{Cu}}_2\text{O}$ precipitate but does not react with ketones.

$\therefore$ P gives a positive Fehling test; Q gives a negative Fehling test. Fehling solution distinguishes them.

2,4-DNP and ${\text{NaHSO}}_3$ react with both aldehydes and ketones, so they cannot distinguish. Lucas reagent is for alcohols.