See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Step 1 — Concept: The equilibrium constant for hydration (K_hyd) of a carbonyl compound (aldehyde or ketone) with water to form a geminal diol depends on (a) steric effects and (b) electronic effects, as well as (c) ring strain relief. Step 2 — Steric effects: Bulkier substituents around the carbonyl carbon disfavor the addition of water because the sp2 → sp3 rehybridization increases steric crowding. Compound 3, di-tert-butyl ketone, has two extremely bulky tert-butyl groups flanking the carbonyl carbon, making nucleophilic addition very difficult. This gives compound 3 the smallest K_hyd. Step 3 — Ring strain effects: When a cyclic ketone undergoes hydration, the ring strain in the sp2 carbonyl-containing ring is partly relieved upon going to the sp3 geminal diol. Cyclopropanone (compound 2) has very high ring strain (~115 kJ/mol) in the sp2 ring; relief of this strain upon hydration strongly favors the product, giving compound 2 the largest K_hyd. Cyclobutanone (compound 1) also benefits from ring strain relief, but less so than cyclopropanone. Step 4 — Electronic effects: In cyclopropanone, the C–C–C angle is forced to ~60°, which means the carbonyl carbon uses orbitals with more p-character, and the Walsh orbital interactions make the carbonyl more electrophilic, further increasing K_hyd relative to cyclobutanone. Step 5 — Ranking: Compound 3 (di-tert-butyl ketone) has the smallest K_hyd due to severe steric hindrance. Compound 1 (cyclobutanone) has an intermediate K_hyd. Compound 2 (cyclopropanone) has the largest K_hyd due to maximum ring strain relief and enhanced electrophilicity. Order of increasing K_hyd: 3 < 1 < 2, which corresponds to answer choice (b). Why other options fail: - (a) 1 < 2 < 3: Incorrect because compound 3 should have the smallest K_hyd, not the largest. - (c) 2 < 1 < 3: Incorrect; cyclopropanone has the highest K_hyd, not the lowest. - (d) 2 < 3 < 1: Incorrect; cyclopropanone has the highest K_hyd, not the lowest. Therefore, the correct answer is B.