See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: Carbonyl compounds form gem-diol hydrates upon addition of water. The stability of these hydrates depends on the degree of electrophilicity of the carbonyl carbon and the steric/electronic factors that stabilize or destabilize the sp3 gem-diol product relative to the sp2 carbonyl. Step 1 - General principle: Hydrate (gem-diol) formation is favored when the carbonyl carbon is highly electrophilic (electron-withdrawing groups nearby) and when there is little steric hindrance. Hydrates are stable when the carbonyl is activated by electron-withdrawing substituents or when ring strain relief occurs upon going from sp2 to sp3. Step 2 - Option (a) Ph-CO-CO-CO-Ph (triketone): The central carbonyl is flanked by two electron-withdrawing acyl groups (PhCO- on each side), making the central carbonyl extremely electrophilic. Such 1,2,3-triketones readily form stable hydrates at the central carbonyl. FORMS stable hydrate. Step 3 - Option (b) Indane-1,3-dione: This is a cyclic 1,3-diketone in a five-membered ring fused to benzene. The two flanking carbonyls strongly activate the C2 position (active methylene), and the compound can form a stable hydrate or undergoes enolization. More importantly, 1,3-diketone systems with flanking carbonyls stabilize hydrates well. Additionally, this compound is known to form a stable hydrate. FORMS stable hydrate. Step 4 - Option (c) Cyclopropanone: The three-membered ring has significant ring strain. The carbonyl carbon in cyclopropanone is highly electrophilic due to the ring geometry (more s-character in C-C bonds, making substituents more electron-withdrawing). Cyclopropanone readily and stably forms a hydrate (cyclopropane-1,1-diol). Ring strain relief upon going from sp2 (planar) to sp3 also helps. FORMS stable hydrate. Step 5 - Option (d) Cyclohexanone: This is a simple unstrained cyclic ketone. The carbonyl carbon has no electron-withdrawing substituents to enhance electrophilicity, and there is moderate steric hindrance. Simple dialkyl ketones (and cyclic ketones like cyclohexanone) do NOT form stable hydrates under normal conditions - the equilibrium strongly favors the ketone form over the gem-diol. Does NOT form a stable hydrate. Step 6 - Comparison: Among the options, cyclohexanone is a plain dialkyl ketone with no activating groups, and it is well established that simple ketones do not form isolable, stable hydrates. The other three options have special features (flanking carbonyls, ring strain) that favor stable hydrate formation. Therefore, the correct answer is D.