Compound having a hydroxyl group directly attached to a benzene ring are called phenols. The term phenol is also used for the parent compound, hydroxybenzene. Hydroxybenzene, may be regarded as an enol, as implied by the name phenol, from phenyl + enol. However unlike simple ketones, which are far more stable than their corresponding enols, the analogous equilibrium for phenol lies far on the side of the enol form. The reason for this difference is the resonance energy of the aromatic ring, which provides an important stabilization of the enol form.
Since the functional group occurs as suffix in phenol, many compounds containing hydroxyl group are named as derivatives of the parent compound phenol, as illustrated by the IUPAC names.
Suffix groups such as sulfonic acid and carboxylic acid take priority, and when these groups are present the hydroxyl group is used as a modifying prefix.
Phenyl ethers are named in the IUPAC system as alkoxyarenes, although the ether nomenclature is used for some compounds.
Phenols and their ethers are widespread in nature, and, as is usual for such compounds, trivial names abound.
The methyl phenols are commonly called cresols.
The benzene diols also have common names
Salts of Phenols :
Phenols are fairly acidic compounds, and in this respect, markedly different from alcohols, which are even more weakly acidic than water. Aqueous hydroxides converts phenols into their salts, aqueous mineral acid convert the salts back into the free phenols.
Most phenols have Ka values in the neighbourhood of 10−10 and are thus weaker acids than the carboxylic acids (Ka values about 10−5). Most phenols are weaker than carbonic acid and hence unlike carboxylic acids do not dissolve in aqueous bicarbonate solution.