JEE Main · 2025 · 23 Jan 2025 · Shift 2 · Aldehydes Ketones and Carboxylic Acids

Aldehyde hydration, $\mathrm{R}{}_2\mathrm{C}=\mathrm{O}+\mathrm{H}{}_2\mathrm{O}\rightleftharpoons \mathrm{R}{}_2\mathrm{C}(\mathrm{OH}){}_2$, is favoured by anything that makes the carbonyl carbon more electrophilic or more accessible to water. Formaldehyde carries only two hydrogens as substituents, so steric hindrance to the approach of water is negligible, giving it one of the largest hydration constants among common aldehydes ($K\approx 2280$) — Statement I is correct. Trichloroacetaldehyde (chloral) carries three strongly electron-withdrawing chlorine atoms whose $-I$ effect pulls electron density away from the carbonyl carbon, making it more electrophilic and favouring hydration despite the added bulk, giving $K\approx 2000$ — Statement II is correct. Both statements correctly account for the large hydration constants of these two aldehydes.