Hemiacetal

They generally result from the nucleophilic addition of an alcohol (a compound with at least one hydroxy group) to an aldehyde (R−CH=O) or a ketone (R2C=O) under acidic conditions.

Hemiacetals can be strategically used as a protecting group for carbonyls in organic synthesis to prevent unwanted reactions from occurring.

The desired reaction with the target functional group can then be carried out, and the hemiacetal can later be converted back to a carbonyl via hydrolysis.

Tetrahydrofurans can be synthesized from nucleophilic addition to hemiacetals with high stereoselectivity, which can be further used to form polymers such as lignans.

[10] Drug discovery programs synthesize spiroacetal scaffolds to generate libraries of spiroacetal-containing molecules.

Hemiacetal esters are primarily used in polymer chemistry as a polymerization initiator and as a protecting group for carboxylic acids.

The general structure of a hemiacetal (left) and hemiketal (right).
Formation of a general cyclic hemiacetal
Structures of some readily isolable hemiacetals and hemiketals. Chloral and ethyl glyoxalate illustrate the stabilizing influence of electron-withdrawing groups. The cyclopropanone case illustrates the effect of ring-strain . [ 7 ] The two cases on the right illustrate the effect of ring-closure. [ 5 ]