Carboxyl group

A functional group in which a carbonyl group and a hydroxyl group are attached to the same carbon atom, commonly written –COOH. It can donate a proton, forming a carboxylate ion.

Carboxylic acid: An organic compound containing one or more carboxyl groups. The carboxyl group is the defining functional group of this compound family.
Carbonyl group: A functional group consisting of a carbon atom double-bonded to oxygen. The carbonyl is one of the two linked groups that define the carboxyl structure.
Amino acid: An organic molecule containing amino and carboxyl groups, with side chains that vary among amino acids. Amino acids use their carboxyl groups in peptide-bond formation and acid–base chemistry.
Alcohol: An organic compound containing a hydroxyl group bonded to a saturated carbon atom. Unlike an alcohol hydroxyl, the carboxyl hydroxyl shares a carbon with a carbonyl.
Carboxylate: An ion or salt formed when a carboxylic acid loses a proton. Deprotonation converts the group into its resonance-stabilized, negatively charged form.
Hydroxyl group: An –OH group consisting of oxygen bonded to hydrogen. The hydroxyl is attached to the carbonyl carbon in a carboxyl group.
Fatty acid: A carboxylic acid with a hydrocarbon chain, found in fats and other lipids. Its carboxyl group anchors the polar end of an otherwise largely nonpolar molecule.
Phenol: An aromatic compound with a hydroxyl group directly bonded to an aromatic ring. Phenols can be acidic, but their hydroxyl group is not part of a carboxyl group.
Resonance: A way to represent electron delocalization using multiple Lewis structures that differ only in electron placement. Electron delocalization across the carboxylate explains why its two C–O bonds become similar.
Covalent bond: A chemical bond formed when atoms share pairs of electrons. The group’s shape and reactivity arise from its shared-electron bonds.

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