acyl

An acyl group is a functional group in organic chemistry with the general formula R-CO-, where R is an alkyl or aryl substituent. It is derived from a carboxylic acid by removal of the hydroxyl group, and it is the key reactive fragment in a wide range of acylation reactions. The carbonyl carbon is double-bonded to oxygen and singly bonded to R and to the substituent that attaches the acyl unit to the rest of the molecule. When used as a substituent, the acyl group is often named with the suffix -oyl (for example acetyl, benzoyl, palmitoyl).

Common acyl-containing derivatives include acyl chlorides (R-COCl), anhydrides (R-CO-O-CO-R'), esters (R-COOR'), and amides (R-CO-NR'R''). Thioesters (R-CO-SR') and acyl phosphates also exist. The reactivity of these groups varies widely; acyl chlorides and anhydrides are highly reactive, while simple carboxylic acids require activation for efficient transfer of the acyl unit.

In synthesis, acyl groups are transferred to oxygen, nitrogen, or carbon centers to form esters, amides, and anhydrides. In organic chemistry, acylation reactions are widely used to introduce carbonyl-containing fragments into molecules. Friedel-Crafts acylation, for example, uses an acyl halide and a Lewis acid catalyst to attach an acyl group to an aromatic ring, yielding aryl ketones.

In biochemistry, acyl groups are carried by cofactors such as acyl-CoA and acyl carrier proteins, enabling fatty acid metabolism and the transfer of acyl units in biosynthetic pathways.