Carboxil

Carboxil, also known as the carboxyl group, is a principal functional group in organic chemistry with the formula -COOH. It consists of a carbonyl group (C=O) and a hydroxyl group (−OH) attached to the same carbon atom. In many contexts, the term carboxil is used interchangeably with carboxyl, and it is a defining feature of carboxylic acids, where the group is present as part of a larger molecule R–COOH.

The carboxyl group is characterized by resonance between the two oxygen atoms, which distributes electron density and stabilizes both the neutral carboxylic acid and its conjugate base. In solution, carboxylic acids can donate a proton to form the carboxylate anion (R–COO−); this acidic behavior is responsible for the weakly acidic character of these compounds. Typical pKa values are around 4–5 for many simple carboxylic acids, though they vary with substituents and solvent.

Reactions involving the carboxyl group are central to organic synthesis. Esters form when carboxylic acids react with alcohols (esterification) in the presence of an acid catalyst, producing R–COOR and water. Amide formation occurs when carboxylic acids or derivatives react with amines, often with coupling reagents. Carboxylic acids also form acid chlorides, anhydrides, and undergo decarboxylation under certain conditions. In biological systems, the carboxyl group is key in constituting amino acids, fatty acids, and many metabolites.

Nomenclature and examples: in IUPAC naming, the carboxyl group is the suffix -carboxylic acid (as part of the parent chain, e.g., ethanoic acid). The carboxyl group can be present as a neutral group in molecules or as the carboxylate anion in salts.