JEE Main · 2026 · 23 Jan 2026 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

Propanenitrile with stannous chloride and hydrogen chloride, followed by hydrolysis (Stephen reduction), gives propanal, ${\text{CH}}_3{\text{CH}}_2\text{CHO}$ (x). Ozonolysis of but-2-ene followed by hydrolysis cleaves the double bond to give two molecules of acetaldehyde, ${\text{CH}}_3\text{CHO}$ (y). With alkali and heat the two aldehydes undergo aldol condensation; both have $\alpha$-hydrogens, so four $\alpha ,\beta$-unsaturated aldehydes are possible. Self-condensation of acetaldehyde gives but-2-enal, self-condensation of propanal gives 2-methylpent-2-enal, addition of the propanal enolate to acetaldehyde gives 2-methylbut-2-enal, and addition of the acetaldehyde enolate to propanal gives pent-2-enal. The branched aldehyde 3-methylbut-2-enal, $({\text{CH}}_3{)}_2\text{C}=\text{CH-CHO}$, cannot arise from these partners and is not obtained.