A
hydroxyl or
hydroxy group is a chemical
functional group containing one
oxygen atom connected by a
covalent bonding to one
hydrogen atom (-OH). It is sometimes called the
alcohol functional group because when bonded to carbon in a molecule that otherwise contains only hydrogen and carbon the hydroxy (not hydroxyl) group defines the molecule as an alcohol, resulting in a name ending in -ol. A hydroxyl group bonded covalently to the carbon of a
carbonyl group (C=O) produces a
carboxyl group (C(O)OH) that is the defining group of a carboxylic acid. When the -OH group participates in an ionic bond, the [OH
-] anion is called the
hydroxide ion. As a
free radical, it is the
hydroxyl radical.