The phenol functional group is an -OH attached to a benzene ring. There may be one or more hydroxyl molecules attached to the ring structure.

The phenol functional group is acidic. Phenol-containing compounds are soluble in alkalis, producing the appropriate metallic salt in a compound called a phenate. Phenol-containing compounds are unusual amongst organic compounds because of their solubility in water. This solubility increases if more hydroxyl groups are added to the ring structure. The solubility is due to hydrogen bonding. The simplest compound containing the phenol group is actually called phenol, it has the formula C₆H₅OH. The phenolic group is C₆H₄OH. The phenol functional group is phenol with the loss of one hydrogen producing a negatively charged molecule.

Phenol was originally isolated from coal tar in 1834 by Friedlieb Ferdinand Runge (1795-1867), who named it carbolic acid. The name phenol...