carbonylgrupper

The carbonyl group, denoted as C=O, is a functional group consisting of a carbon atom double-bonded to an oxygen atom. It is a defining feature of many organic compounds and appears in aldehydes, ketones, carboxylic acids and their derivatives, and many other functional classes such as esters, amides, and anhydrides.

Structurally, the carbonyl carbon is typically sp2-hybridized and the C=O bond is planar, with the three surrounding substituents arranged roughly 120 degrees apart. The carbonyl bond is highly polar, giving the oxygen a partial negative charge and the carbon a partial positive charge. This polarity manifests in characteristic infrared absorption near the carbonyl stretch region, around 1650–1750 cm−1, depending on the specific compound and conjugation.

Common categories include aldehydes (R-CHO) and ketones (R-CO-R′), which contain the carbonyl group itself, and carboxylic acids and their derivatives (esters, amides, anhydrides, acyl chlorides). In these derivatives, the carbonyl carbon remains the reactive site, but substituents on the group influence reactivity and leaving-group ability.

Reactivity is dominated by electrophilicity at the carbonyl carbon. Nucleophiles attack the carbonyl carbon to form a tetrahedral intermediate, enabling reactions such as nucleophilic addition to aldehydes and ketones, and acyl substitution in carboxylic derivatives. Reductions convert carbonyls to alcohols, while oxidation of aldehydes yields carboxylic acids or related species.

Carbonyl groups are widespread in biology and industry, appearing in sugars, proteins, hormones, and many polymers and fragrances. They play key roles in metabolic pathways and in various synthetic transformations.