carboxyls

Carboxyls refer to carboxyl groups, functional groups characterized by a carbon atom double-bonded to an oxygen atom and singly bonded to a hydroxyl group, giving the formula -COOH. In many contexts the term also encompasses the carboxylate form, -COO−, which arises when the acidic proton is lost. The carboxyl group is a defining feature of carboxylic acids, a broad class of organic compounds.

The carboxyl group exhibits resonance between two canonical forms, which delocalizes negative charge in carboxylates and stabilizes the group. This stabilization underlies the relatively high acidity of carboxylic acids (typical pKa around 4–5 in water) and the tendency to form salts with bases. The presence of -COOH affects solubility, hydrogen bonding, and reactivity.

Carboxyl-containing compounds are ubiquitous: simple acids such as formic and acetic acids; aromatic acids like benzoic acid; and large biological molecules such as amino acids (which carry both a carboxyl and an amino group) and fatty acids. The carboxyl group participates in characteristic reactions, including esterification with alcohols to make esters, and amide formation with amines; hydrolysis of esters regenerates carboxylic acids. In basic or thermal conditions, carboxyl groups can undergo decarboxylation, releasing CO2.

Nomenclature notes: the parent class is carboxylic acids; the carboxylate anion is used in salts (e.g., sodium acetate). In many contexts, “carboxyls” indicate the functional group’s role in structure and reactivity within organic and biological chemistry.