Answer: the -OH of the acid and -H of ethanol.
- A the -OH of ethanol and -H of the acid
- B both oxygens of the acid
- C the -OH of the acid and -H of ethanol
- D the alcohol oxygen only
Correct answer: C. the -OH of the acid and -H of ethanol
Explanation: Isotopic labelling shows acyl-oxygen cleavage: the -OH comes from the acid and the -H from the alcohol, so the ester oxygen is the alcohol oxygen.
Curved arrows show the nucleophile attacking the carbonyl carbon while the C=O pi electrons move onto oxygen, giving a tetrahedral alkoxide intermediate.
Concept context
Aldehydes, ketones, carboxylic acids, and their derivatives (esters, amides, acid chlorides). Key reactions include nucleophilic addition, Aldol condensation, Cannizzaro, and Claisen. Very heavily tested in JEE and NEET.
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