karboksyyliryhmätyyppeihin

The carboxyl group, sometimes referred to in Finnish as karboksyyliryhmä, is a functional group in organic chemistry with the formula -COOH. It consists of a carbonyl carbon double-bonded to an oxygen atom and single-bonded to a hydroxyl group. Through resonance, the group can be described as -COOH or the deprotonated form -COO−, which is the conjugate base of a carboxylic acid. This resonance imparts characteristic acidity and stabilizes the carboxylate anion.

Carboxylic acids are weak acids. In aqueous solution they donate a proton to yield the carboxylate anion and a hydronium ion, with pKa values typically around 4–5, depending on substituents. The carboxylate anion is stabilized by resonance, contributing to the acidity and to the solubility of small acids in water.

The carboxyl group participates in many important reactions. Esterification with alcohols forms esters, usually under acidic catalysis (Fischer esterification). Reaction with amines yields amides. Converting to derivatives such as acid chlorides enables formation of anhydrides, esters, and amides. Carboxyl groups can be decarboxylated upon heating or in the presence of catalysts and can be reduced to primary alcohols with strong reducing agents. In metabolism, carboxyl groups appear in fatty acids and amino acids, where they contribute to energy storage, structural roles, and biochemical reactivity.

Carboxyl groups are ubiquitous in organic chemistry and biochemistry, underpinning a wide range of synthetic transformations and biological processes.