Illustrated Glossary of Organic Chemistry

Hemiacetal: A functional group containing an ether group and a hydroxyl group bonded sharing a carbon atom.

General hemiacetal structure. When R1 and R2 are carbon groups this functional group is sometimes referred to by the outdated term hemiketal (because this hemiacetal is derived from a ketone instead of an aldehyde).

2-Methoxypropan-2-ol, a hemiacetal.

Maltose (a disaccharide) contains a hemiacetal and an acetal.