CH3CO

CH3CO is a shorthand notation for the acetyl group, the acyl substituent derived from acetic acid (ethanoic acid). The fragment consists of a methyl group (CH3) linked to a carbonyl carbon (C=O) and is often written as CH3-CO-. In many contexts the acetyl group has the molecular formula C2H3O.

In chemical reactions the acetyl group is attached to various atoms or groups through the carbonyl carbon, forming acetyl derivatives such as acetyl chloride (CH3COCl), and acetic anhydride ((CH3CO)2O). It is a common building block in organic synthesis and participates in a range of acylation reactions, including Friedel–Crafts acylation and the acetylation of alcohols and amines.

In biology the acetyl group is transferred by coenzyme A to form acetyl-CoA, a central metabolite in the citric acid cycle and in fatty acid synthesis. Acetylation of histones is an epigenetic mechanism that regulates gene expression by modifying chromatin structure.

Properties and handling: the acetyl fragment itself is not typically isolated as a stable neutral molecule; derivatives and salts of acetyl are more commonly encountered. When discussing reactive intermediates, CH3CO• denotes the acetyl radical, a highly reactive species.

See also: acetate, acetyl chloride, acetyl-CoA, acetylation, acetic acid.