Carbonyl group

In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containing a carbonyl group is often referred to as a carbonyl compound.

The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex (a metal carbonyl, e.g. nickel carbonyl).

The remainder of this article concerns itself with the organic chemistry definition of carbonyl, where carbon and oxygen share a double bond.

Carbonyl compounds

A carbonyl group characterizes the following types of compounds:

CompoundAldehydeKetoneCarboxylic acidCarboxylate EsterAmide
CompoundEnoneAcyl halideAcid anhydrideImide
General formulaRC(O)C(R')CR''R'''RCOX(RCO)2ORC(O)N(R')C(O)R''

Note that the most specific labels are usually employed. For example, R(CO)O(CO)R' structures are known as acid anhydride rather than the more generic ester, even though the ester motif is present.

Other organic carbonyls are urea and the carbamates, the derivatives of acyl chlorides chloroformates and phosgene, carbonate esters, thioesters, lactones,