See image — Alcohols Phenols and Ethers Chemistry Question

💡 Solution & Explanation

Step 1: Identify reagents A and B from the first reaction. H2O^18 reacts with Na (a base context) to form NaO^18H (sodium hydroxide with O-18) as product (A) and H2 gas as product (B). So A = Na^18OH (NaO^18H). Step 2: Identify the second reaction. Ethyl acetate (CH3-C(=O)-O-CH2-CH3) reacts with NaO^18H (A) in a base-catalyzed hydrolysis (saponification). Step 3: Mechanism of saponification with labeled hydroxide. In saponification, the labeled ^18OH^- (nucleophile) attacks the carbonyl carbon of the ester. The acyl-oxygen bond (between the carbonyl carbon and the oxygen attached to the ethyl group) breaks. This means the ^18O from the hydroxide ends up on the carbonyl carbon, forming the carboxylate product. The products are: - The carboxylate salt: CH3-C(=O)-^18O^- (acetate with ^18O on the single-bond oxygen, i.e., the oxygen that came from the nucleophile) — but actually the carboxylate is resonance-stabilized, and the ^18OH attacks the carbonyl, so the carboxylate has one ^18O. - Ethanol (D): CH3CH2-OH (the leaving group retains the original ester oxygen). Step 4: Determine product C. The carboxylate formed is CH3-C(=O)-^18O^- (sodium salt form would be with Na^+, but in the context of the reaction with NaO^18H, the product C is the carboxylate anion/sodium salt). However, looking at option (c): CH3-C(=O)-^18O^- — this shows acetate anion where the single-bond oxygen bears the ^18O label. This is consistent with the ^18OH^- attacking the carbonyl carbon and the acyl-oxygen bond (C-O of the ethyl ester) cleaving, leaving the ^18O incorporated into the carboxylate. Step 5: Why other options fail. (a) CH3-C(=O)-^18O-H: This would be acetic acid with ^18O on the hydroxyl, which would require protonation and also places ^18O on the -OH, which is consistent structurally, but the reaction gives the sodium salt (carboxylate), not the free acid. (b) CH3-C^18(=O)-O-H: This would require ^18O in the carbonyl position, which is not where the nucleophilic ^18OH ends up in direct attack — the nucleophile oxygen becomes the single-bond oxygen after the tetrahedral intermediate collapses. (d) CH3-C(=O)-O^- Na^+: This is the unlabeled acetate sodium salt, which does not show the ^18O label at all. Option (c) correctly shows the acetate carboxylate anion with ^18O on the single-bond oxygen position (the oxygen derived from the ^18OH^- nucleophile), which is the correct product of saponification with labeled hydroxide. Therefore, the correct answer is C.