A ketone compound containing a carbonyl group (C=O)
A ketone compound containing a carbonyl group (C=O)

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.[1]

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

See also: α,β-Unsaturated carbonyl compound

In organic chemistry, a carbonyl group characterizes the following types of compounds:

Compound Aldehyde Ketone Carboxylic acid Carboxylate ester Amide
Carboxylic acid
Compound Enone Acyl halide Acid anhydride Imide
Acyl chloride
Acid anhydride
General formula RC(O)C(R')CR''R''' RCOX (RCO)2O RC(O)N(R')C(O)R''
Carbon dioxide
Carbon dioxide

Other organic carbonyls are urea and the carbamates, the derivatives of acyl chlorides chloroformates and phosgene, carbonate esters, thioesters, lactones, lactams, hydroxamates, and isocyanates. Examples of inorganic carbonyl compounds are carbon dioxide and carbonyl sulfide.[citation needed]

A special group of carbonyl compounds are dicarbonyl compounds, which can exhibit special properties.

Structure and reactivity

For organic compounds, the length of the C-O bond does not vary widely from 120 picometers. Inorganic carbonyls have shorter C-O distances: CO, 113; CO2, 116; and COCl2, 116 pm.[2]

The carbonyl carbon is typically electrophilic. A qualitative order of electrophilicity is RCHO (aldehydes) > R2CO (ketones) > RCO2R' (esters) > RCONH2 (amides). A variety of nucleophiles attack, breaking the carbon-oxygen double bond.

A carbonyl compound
A carbonyl compound

The polarity of C=O bond also enhances the acidity of any adjacent C-H bonds. The pKa values of acetaldehyde and acetone are 16.7 and 19 respectively,[3]


See also


  1. ^ Saul Patai, ed. (1966). The Carbonyl Group. PATAI'S Chemistry of Functional Groups. Vol. 1. John Wiley & Sons. doi:10.1002/9780470771051. ISBN 9780470771051.Jacob Zabicky, ed. (1970). The Carbonyl Group. PATAI'S Chemistry of Functional Groups. Vol. 2. John Wiley & Sons. doi:10.1002/9780470771228. ISBN 9780470771228.
  2. ^ G. Berthier, J. Serre (1966). "General and Theoretical Aspects of the Carbonyl Goup". In Saul Patai (ed.). The Carbonyl Group. PATAI'S Chemistry of Functional Groups. Vol. 1. John Wiley & Sons. p. 1-77. doi:10.1002/9780470771051.ch1. ISBN 9780470771051.
  3. ^ Ouellette, R.J. and Rawn, J.D. "Organic Chemistry" 1st Ed. Prentice-Hall, Inc., 1996: New Jersey. ISBN 0-02-390171-3
  4. ^ Mayo D.W., Miller F.A and Hannah R.W “Course Notes On The Interpretation of Infrared and Raman Spectra” 1st Ed. John Wiley & Sons Inc, 2004: New Jersey. ISBN 0-471-24823-1.
  5. ^ "Archived copy" (PDF). Archived from the original (PDF) on 2015-08-24. Retrieved 2015-07-11.((cite web)): CS1 maint: archived copy as title (link)

Further reading