Question

When butanoic acid and 18_O-labelled methanol react under acidic conditions, what compounds are labelled when the reaction has reached equilibrium?

Short answer

Mechanism followed as:

Step-by-step solution

Reaction of carboxylic acid with alcohol

When carboxylic acid reacts with alcohol formation of ester and the water occur and the oxygen of the carboxylic acid is leave in the form of water molecule.

Reaction of butanoic acid with methanol

when butanoic acid reacts with alcohol the carbonyl of the acid accepts the proton and then hydroxyl oxygen attack on carbonyl carbon followed by again protonation formation of -OH₂ which is a best leaving group and that is the carboxylic acid oxygen which accepts the proton hence, labelled 18_Ois present in the water