Sodium borodeuteride is a commercially available reducing reagent that can convert aldehydes and ketones to the corresponding alcohols along with an isotopic label. draw the reaction between benzaldehyde and sodium borodeuteride showing the position of isotopic labeling.

Here we have to draw the mechanism of the reduction reaction between benzaldehyde and sodium borodeuteride to form the corresponding alcohol.

The reducing agent sodium borodeuteride can reduce the aldehydes to its corresponding alcohol. The reaction mechanism is shown in the attached image.

The reaction mechanism can be explained as-

The sodium borodeuteride is highly ionic in nature thus it remains as Na⁺ and BD₄⁻ The deuterium atom of BD₄⁻ attack the carbonyl carbon atom and substitute one of its deuterium as shown in the figure.

One molecule of sodium borodeuteride can reduce four molecules of benzaldehyde. The polar solvent like alcohol donates the proton as shown in the mechanism.

The converted alcohol contains the deuterium atom at the -C center. Thus benzaldehyde is converted to deuteroted benzyl alcohol.

the answer is a! (2.9 x 10^-18 j) hope i could someone. : )