Hemiacetal

Hemiacetals (or hemiacetals ) are chemical compounds that are characterized by an alkoxy or aryloxy group - OR, and a hydroxyl group -OH which are bonded to the same carbon atom. Hemiacetals are formed as intermediate in the acetal formation, by reacting an alcohol or acid - base catalysis is added to a carbonyl group. Under the action of strong acids is an acetal formed by reaction with a further molecule of alcohol last. They have the general structure R1R2C (OH) OR, where R may be a H. Cyclic hemiacetals are called lactols.

Natural Products

Various sugars are aldoses, such as D-glucose. The aldoses are often present as cyclic hemiacetals.

Education

Hemiacetals are an intermediate stage on the way to acetals.

Dithiohalbacetale

If the two oxygen atoms are replaced by sulfur atoms formally in hemiacetals obtained Dithiohalbacetale. In the synthesis of the natural product erythromycin Dithiohalbacetal played a central role.