See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: Hydrate formation (gem-diol formation) from an aldehyde or ketone involves nucleophilic addition of water to the carbonyl carbon. The equilibrium constant for hydrate formation increases as the carbonyl carbon becomes more electrophilic (more electron-deficient). Electron-withdrawing groups (EWGs) increase the electrophilicity of the carbonyl carbon and favor hydrate formation (larger K), while electron-donating groups (EDGs) decrease electrophilicity and disfavor hydrate formation (smaller K). Reasoning: - All four compounds are alpha-tetralone (3,4-dihydronaphthalen-1(2H)-one) derivatives with the ketone carbonyl at C1. - The substituents on the aromatic ring influence the electron density at the carbonyl carbon through resonance and inductive effects. Compound I: NH2 at C6 (para-like position relative to carbonyl through the ring). NH2 is a strong electron-donating group (EDG) via resonance, which increases electron density at the carbonyl carbon, making it less electrophilic. This greatly disfavors hydrate formation → smallest K. Compound II: NH2 at C5 (meta-like position relative to carbonyl, but closer/ortho to carbonyl side). NH2 is still an EDG, but at this position its resonance donation to the carbonyl is slightly less effective than at C6 (para). However, it is still electron-donating, so K is small but slightly larger than compound I. Compound III: Unsubstituted tetralone. No substituent effect, intermediate electrophilicity of carbonyl → intermediate K. Compound IV: NO2 at C6 (para-like position relative to carbonyl). NO2 is a strong electron-withdrawing group (EWG) via resonance and induction, which decreases electron density at the carbonyl carbon, making it more electrophilic. This strongly favors hydrate formation → largest K. Increasing order of K: I < II < III < IV This matches option (c). Why other options fail: - Option (a) IV < III < II < I: This is the reverse order, incorrectly placing EWG compound last. - Option (b) IV < III < I < II: Also reverses the expected trend for EWG vs EDG. - Option (d) II < III < I < IV: Incorrectly orders the two amino compounds relative to unsubstituted. Therefore, the correct answer is C.