See image — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Concept: In polar protic solvents, nucleophilicity is governed by two main factors: (1) polarizability of the nucleophilic atom, and (2) resonance stabilization (delocalization) of the lone pair, which reduces nucleophilicity. Step 1 – Identify the nucleophilic atoms and their environments: - Species (1): CH3CH2CH2O^- — propoxide ion; nucleophilic atom is oxygen, a localized carbanion-like alkoxide with concentrated negative charge. - Species (2): CH3CH2CH2S^- — propanethiolate ion; nucleophilic atom is sulfur, which is in the third period and is much more polarizable than oxygen. - Species (3): CH3CH2C(=O)O^- — propanoate ion (carboxylate); nucleophilic atom is oxygen, but the negative charge is delocalized over two oxygen atoms via resonance with the carbonyl group. Step 2 – Apply polarizability effect (critical in polar protic solvents): In polar protic solvents, larger, more polarizable atoms are better nucleophiles because they are less tightly solvated. Sulfur (3rd period) is far more polarizable than oxygen (2nd period). Therefore, species (2) CH3CH2CH2S^- is the best nucleophile. Step 3 – Compare the two oxygen nucleophiles: - Species (1) CH3CH2CH2O^- has a localized negative charge on one oxygen atom — it is a strong nucleophile. - Species (3) CH3CH2C(=O)O^- has its negative charge delocalized by resonance over two oxygen atoms — this significantly reduces nucleophilicity. Therefore, (1) > (3) in nucleophilicity. Step 4 – Compile the ranking: 2 > 1 > 3 (most to least nucleophilic) Step 5 – Evaluate the options: (a) 3 > 1 > 2 — Incorrect; ignores polarizability and resonance effects. (b) 2 > 3 > 1 — Incorrect; ranks carboxylate above alkoxide, which is wrong. (c) 1 > 3 > 2 — Incorrect; places sulfur last, ignoring its superior polarizability. (d) 2 > 1 > 3 — Correct; sulfur nucleophile first (polarizability), then alkoxide (localized charge), then carboxylate (resonance-delocalized, least nucleophilic). Therefore, the correct answer is D.