Chapter 17, Problem 17.6P

Interpretation Introduction

(a)

Interpretation:

The major organic product of the given reaction is to be predicted.

Concept introduction:

${\text{NaBH}}_{\text{4}}$ can be used as a reducing agent to convert a ketone to a secondary alcohol and an aldehyde to a primary alcohol. ${\text{NaBH}}_{\text{4}}$ gives a hydride ion. ${\text{H}}^{\text{-}}$ undergoes nucleophilic addition to the electron-poor carbonyl carbon to produce a strongly basic alkoxide anion. In the second step, a molecule of water or alcohol that is already present as the solvent protonates the alkoxide anion to produce the final product, an alcohol. ${\text{NaBH}}_{\text{4}}$ is not highly basic and can tolerate a weakly acidic solvent like water or alcohol.

Interpretation Introduction

(b)

Interpretation:

The major organic product of the given reaction is to be predicted.

Concept introduction:

${\text{LiAlH}}_{\text{4}}$ is used as a reducing agent to convert a ketone to a secondary alcohol and an aldehyde to a primary alcohol. ${\text{LiAlH}}_{\text{4}}$ is a yields a hydride ion. This produces an alkoxide ion, which, on protonation, gives the final product, an alcohol.

${\text{LiAlH}}_{\text{4}}$ is, however, strongly basic and reacts with most acids, often violently. It will react with even weakly acidic solvents like water or alcohol rather than the substrate. Therefore, the solvent must be an aprotic solvent like ether, and the second-step protonation cannot be done till the first step is complete.