What is "hemiacetal"

n. (context chemistry English) Any of a class of compounds of general formula R₂C(OH)OR' (where R' is not H).

n. an organic compound usually formed as an intermediate product in the preparation of acetals from aldehydes or ketones

Hemiacetals and hemiketals are compounds that are derived from aldehydes and ketones respectively. The Greek word hèmi means half. These compounds are formed by formal addition of an alcohol to the carbonyl group.

When the alcohol group is replaced by a second alkoxy group, an acetal or a ketal, respectively, is formed.