22. Carboxylic Acid Derivatives: NAS

D. N. Kursanov, a Russian chemist, proved that the bond that is broken in the hydroxide-ion-promoted ­hydrolysis of an ester is the acyl C—O bond, rather than the alkyl C—O bond, by studying the hydrolysis of the following ester under basic conditions:

a. What products contained the ¹⁸O label?

b. What product would have contained the ¹⁸O label if the alkyl C—O bond had broken?

The intermediate shown here is formed during the hydroxide-ion-promoted hydrolysis of the ester group. Propose a mechanism for the reaction.