Carbonyl

The carbonyl group is a functional group consisting of a carbon atom double-bonded to an oxygen atom (C=O). It is a central motif in many organic compounds and appears in aldehydes, ketones, carboxylic acids and a wide range of derivatives. The carbonyl carbon is typically sp2-hybridized and lies in a planar arrangement; the C=O bond is highly polar due to the electronegativity of oxygen.

Bond lengths of the C=O bond are about 1.20–1.25 Å, and the group is stabilized by resonance in some derivatives. The polarity creates a dipole moment and makes the carbonyl carbon an electrophilic center susceptible to nucleophilic attack. In aldehydes and ketones, nucleophilic additions are common, while in carboxylic derivatives the chemistry often proceeds via acyl substitution.

Infrared spectroscopy shows a strong C=O stretching vibration, typically around 1700 cm-1, with exact position influenced by conjugation, ring strain, hydrogen bonding, and substituents. Carbonyl compounds can also exhibit keto–enol tautomerism, placing a small amount of population in the enol form under some conditions.

Key classes include aldehydes (R-CHO), ketones (R-CO-R'), carboxylic acids (R-CO2H) and derivatives such as esters (R-CO2R'), amides (R-CONR2), anhydrides and acyl chlorides. Carbonyl groups are common in biology and industry, appearing in sugars, peptide bonds, and numerous metabolic intermediates, as well as in solvents and reagents.

Chemistry of carbonyl compounds encompasses oxidation and reduction, as well as condensation and substitution reactions that form a wide range of products. The carbonyl group therefore plays a foundational role in organic synthesis and biochemistry, providing routes to materials, medicines, and biologically important molecules.