According to the IUPAC nomenclature, monosubstituted benzene derivatives are named by prefixing the substituent's name to the parent benzene. IUPAC has also accepted common names for simple monosubstituted benzene derivatives. For example, toluene for methylbenzene and phenol for hydroxybenzene. Benzene and its alkyl-substituted derivatives are often referred to as arenes. They are named depending on the size of the alkyl group. If the alkyl group has six or fewer carbons, then the arene is termed an alkyl-substituted benzene. Conversely, when the alkyl group has more than six carbons or consists of other functional groups, the benzene ring is treated as a substituent. And the arene is termed a phenyl-substituted compound. The name phenyl, abbreviated as Ph–, represents the C6H5 group of benzene as a substituent, such as in 2-phenylheptane. Similarly, benzyl, abbreviated as Bn–, represents the phenylmethyl group as a substituent, such as in benzyl chloride. Aryl, abbreviated as Ar–, is the substituent derived from an arene after the removal of a hydrogen atom from the aromatic ring.