17.2: Nomenclature of Aromatic Compounds with a Single Substituent

Benzene is the simplest aromatic hydrocarbon or arene. The IUPAC names for simple monosubstituted benzene derivatives are derived by adding the substituent's name as a prefix to the parent benzene. For example, halobenzene, where the halogen could be fluoro (F), chloro (Cl), bromo (Br), and iodo (I).

The naming of aromatic compounds also depends on the chain length of the alkyl group attached to the benzene ring. If the alkyl chain has six or fewer carbons, the compound is named alkyl-substituted benzene. For example, propylbenzene, where the alkyl group has three carbons.

However, if the alkyl chain has more than six carbons or contains other preferential functional groups, the compound is named a phenyl-substituted derivative. The substituent obtained from benzene is termed phenyl (Ph-), whereas that derived from toluene is benzyl (Bn-) groups. For example, 1-phenylheptane, where the alkyl chain has seven carbons,

1-phenyl-1-pentanone with a ketone functional group,

diphenyl ether, where the key functional group is ether,

and benzyl bromide derived from toluene.

In general, the substituents derived from arenes by loss of hydrogen are called aryls. Some of the simple monosubstituted benzene derivatives have acquired common names accepted by IUPAC nomenclature. For example, vinylbenzene is styrene, and isopropylbenzene is cumene. Benzaldehyde and Benzoic acid are other examples.

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.