Karbonylihiilen

Karbonylihiilen is the carbon atom within the carbonyl group C=O of carbonyl compounds such as aldehydes, ketones, carboxylic acids, esters, amides, and anhydrides. In these molecules the carbonyl carbon is the electrophilic center that largely governs the chemistry of the class.

Structure and electronic features: The carbonyl carbon is typically sp2-hybridized, giving a planar arrangement with bond angles close to 120 degrees. The C=O bond is highly polarized, with a partial positive charge on carbon and a partial negative charge on oxygen. Resonance forms place negative charge on oxygen and give the carbonyl carbon a degree of electrophilicity.

Reactivity: The carbonyl carbon readily undergoes nucleophilic attack, forming a tetrahedral intermediate. This underlies many important reactions, including nucleophilic additions to aldehydes and ketones, and acyl substitutions in carboxylic derivatives (esters, acid chlorides, amides). Oxidation of aldehydes can yield carboxylic acids, while reduction can convert carbonyl groups to primary or secondary alcohols. In organic synthesis, common reagents include hydride donors (for example, borohydrides and aluminum hydrides) and organometallic nucleophiles (such as Grignard reagents).

Occurrence and significance: The carbonyl carbon is central in both natural and industrial chemistry. It is a key reactive site in metabolic pathways, polymerization processes (as in polyesters and polyamides), and a wide range of functional-group transformations used in synthesis.

See also: carbonyl group, aldehyde, ketone, carboxylic acid, ester, amide.