Carboxyliques

Carboxyliques, commonly known as carboxylic acids, are a family of organic compounds that contain the carboxyl group, -COOH, attached to a hydrocarbon residue R. Their general formula is R-COOH, where R can be a hydrogen atom (formic acid) or any organic group. The carboxyl group endows these molecules with acidic character and distinct reactivity compared with other organic acids.

The carboxyl group consists of a carbonyl (C=O) and a hydroxyl (O–H) in close proximity. Through resonance, the carboxylate anion formed after deprotonation is stabilized, contributing to the characteristic acidity of carboxylic acids. Most simple carboxylic acids have pKa values around 4–5 in water, making them weak acids but stronger than many other organic acids. They are capable of strong hydrogen bonding, which influences their boiling points and solubility. Smaller carboxylic acids are typically miscible with water, while increasing the size of the hydrocarbon R reduces water solubility and raises boiling points.

Nomenclature follows IUPAC and common usage. The systematic name ends with -anoic acid (for example, ethanoic acid) and many examples include formic, acetic, propionic, and benzoic acids. Longer-chain and branched acids, as well as fatty acids, are common in biology and industry.

Key reactions include esterification with alcohols to form esters, and reaction with bases to yield carboxylate salts. They can be reduced to primary alcohols, and they can undergo decarboxylation or conversion to derivatives such as anhydrides, acyl chlorides, and amides. Carboxylic acids play vital roles in metabolism (for example, citric and fatty acids) and are central to the production of polymers, flavors, and pharmaceuticals.