Question

The following steps are given for the mechanism of esterification of carboxylic acids.
I. The protonated esters looses a proton to give the ester.
II. Protonation of the carbonyl oxygen activates the carbonyl group towards nucleophilic addition of the alcohol.
III. Proton transfer in the tetrahedral intermediate occurs. Arrange the following steps in their correct sequence.

• A. I, II and III
• B. I, III and II
• C. II, III and I
• D. III, II and I

Answer 1

Answer: (C)

Protonation of the carboxyl oxygen activates the carbonyl group toward nucleophilic addition of the alcohol. Proton transfer in the tetrahedral intermediate converts the hydroxyl group into - $-\stackrel{\oplus }{O}{H}_2$ group which being a better leaving group, is eliminated as neutral water molecule. The protonated ester so formed finally loses a proton to give the ester.