Carbonyl
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In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom. The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex (e.g. nickel carbonyl); in this situation, carbon is triple-bonded to oxygen.
A carbonyl group characterizes the following types of compounds (where -CO denotes a C=O carbonyl group):
| Compound | Structure | Formula |
|---|---|---|
| Aldehyde |  |
RCHO |
| Ketone |  |
RCOR' |
| Carboxylic acid |  |
RCOOH |
| Ester |  |
RCOOR' |
| Amide |  |
RCONR'R" |
| Enone |  |
RCOC(R')=CR"R"' |
| Acyl chloride |  |
RCOCl |
| Anhydride |  |
(RCO)2O |
Reactivity
Oxygen is more electronegative than carbon, and thus pulls electron density away from carbon to increase the bond's polarity. Therefore, the carbonyl carbon becomes electrophilic, and thus more reactive with nucleophiles.Carbonyl groups can be reduced by reaction with hydride reagents such as NaBH4 and LiAlH4, and by organometallic reagents such as organolithium reagents and Grignard reagents.
Other important reactions include:
- Wolff-Kishner reduction
- Clemmensen reduction
- Conversion into thioacetals
- Hydration to hemiacetals and hemiketals, and then to acetals and ketals
- Reaction with ammonia and primary amines to form imines
- Reaction with hydroxylamines to form oximes
- Reaction with cyanide anion to form cyanohydrins
- Oxidation with oxaziridines to acyloins
- Reaction with Tebbe's reagent to alkenes.
- perkins reaction
- Tischenko reaction
- Aldol condensation
- Cannizaro's reaction
α,β-Unsaturated carbonyl compounds
α,β-Unsaturated carbonyl compounds are an important class of carbonyl compounds with the general structure Cβ=Cα−C=O. In these compounds the carbonyl group is conjugated with an alkene (hence the adjective unsaturated), from which they derive special properties. Examples of unsaturated carbonyls are acrolein, mesityl oxide, acrylic acid and maleic acid. Unsaturated carbonyls can be prepared in the laboratory in an aldol reaction and in the Perkin reaction. The carbonyl group, be it an aldehyde or acid, draws electrons away from the alkene and the alkene group in unsaturated carbonyls are therefore deactived towards an electrophile such as bromine or hydrochloric acid. As a general rule with unsymmetric electrophiles hydrogen attaches itself at the α position in an electrophilic addition. On the other hand, these compounds are activated towards nucleophiles in nucleophilic addition.Spectroscopy
- Infrared spectroscopy: the C=O double bond absorbs infrared light at wavenumbers between approximately 1680–1750 cm−1. This absorption is known as the "carbonyl stretch" when displayed on an infrared absorption spectrum.
- Nuclear magnetic resonance: the C=O double-bond exhibits different resonances depending on surrounding atoms.
- Mass spectrometry
Other organic carbonyl compounds
Inorganic carbonyl compounds
See also
References
- William Reusch. (2004) [Aldehydes and Ketones] Retrieved 23 May 2005.
- ILPI. (2005) [The MSDS Hyperglossary- Anhydride].
Further reading
- L.G. Wade, Jr. Organic Chemistry, 5th ed. Prentice Hall, 2002. ISBN 013033832X
- The Frostburg State University Chemistry Department. [Organic Chemistry Help] (2000).
- Advanced Chemistry Development, Inc. [IUPAC Nomenclature of Organic Chemistry] (1997).
- William Reusch. [VirtualText of Organic Chemistry] (2004).
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