monocarboxyl

Monocarboxyl refers to chemical compounds that contain exactly one carboxyl group (-COOH). The term is often used to contrast with dicarboxyl and polycarboxyl compounds, which have two or more carboxyl groups. The simplest members of this class are the monocarboxylic acids, also known as carboxylic acids, with the general formula R-COOH. The carboxyl group is highly polar and acidic, enabling hydrogen bonding and acidity in aqueous solution; typical pKa values for simple aliphatic carboxylic acids are around 4.5, meaning they donate a proton in neutral water. In solution, monocarboxyl acids exist in equilibrium between the non-ionized form and the carboxylate anion (R-COO−).

Solubility in water decreases with increasing hydrophobic R group, while many low-molecular-weight examples are miscible or soluble. Examples include formic acid (HCOOH), acetic acid (CH3COOH), propionic acid (C2H5COOH), and benzoic acid (C6H5COOH). Reactions of monocarboxyl acids include esterification with alcohols to form esters, reaction with bases to give carboxylate salts, and conversion to derivatives such as acid chlorides or anhydrides.

Occurrence and uses: carboxyl groups are widespread in biology, appearing in amino acids, fatty acids, and citric acid, among others. In industry, monocarboxyl acids are used as solvents, flavorings, and precursors to esters and various plastics. They also serve as acids in food preservation and as intermediates in chemical synthesis.

See also: carboxylic acid, dicarboxylic acid, polycarboxylate.