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

Verified step by step guidance

1. Identify the ester structure: The ester shown has an O^{18} label on the oxygen atom bonded to the alkyl group.
2. Understand the mechanism: In base-promoted hydrolysis (saponification), the nucleophile (OH^-) attacks the carbonyl carbon, leading to the cleavage of the acyl C—O bond.
3. Determine the products: The acyl C—O bond cleavage results in the formation of a carboxylate ion and an alcohol. The O^{18} label will remain with the alcohol product.
4. Consider the alternative scenario: If the alkyl C—O bond were to break, the O^{18} label would remain with the carboxylate ion instead.
5. Conclude the analysis: The O^{18} label is found in the alcohol product when the acyl C—O bond breaks, and in the carboxylate ion if the alkyl C—O bond were to break.

Key Concepts

Ester Hydrolysis

Ester hydrolysis is a chemical reaction where an ester reacts with water to form an alcohol and a carboxylic acid. In the presence of a base, this reaction is often referred to as saponification. Understanding this process is crucial for determining which bonds are broken and which products are formed, especially when isotopes like O^18 are involved.

Bond Selectivity in Hydrolysis

In ester hydrolysis, the selectivity of bond cleavage is significant. The acyl C—O bond is typically more reactive than the alkyl C—O bond under basic conditions. This concept is essential for understanding why the O^18 label appears in specific products, as it indicates which bond was broken during the reaction.

Isotope Labeling

Isotope labeling involves using isotopes, such as O^18, to trace the movement of atoms through a chemical reaction. In this context, it helps identify which products contain the labeled oxygen after hydrolysis. This technique is valuable for elucidating reaction mechanisms and understanding the pathways of chemical transformations.