Aromatic Compounds (Overview)
Nomenclature of Polysubstituted Aromatic Compounds
The relative position of substituents in double-substituted benzenes is indicated by the prefixes ortho (o), meta (m) and para (p). The substituent's relative position in ortho-substituted benzenes is "1,2". It is "1,3" in meta-substituted benzenes and "1,4" in para-substituted benzenes. The prefixes ortho, meta, and para, or their abbreviations o, m, and p, respectively, are written in italics when used with compound names.
o,m,p-Nomenclature is also commonly used in describing the reactions and their mechanisms of aromatic compounds, when the position in which the reaction takes place must be specified, such as is the case in the sentence "In the catalytic bromination of toluene, bromine reacts in para position...".
Benzene derivatives with more than two substituents are named systematically through the numeration of the substituents' positions. The position numbers must be determined so that they are as small as possible. In the compound name, the substituent names are arranged alphabetically and are prefixed to the parent name.
It is common usage and allowed to use other parent names as benzene, such as toluene, phenol, and benzoic acid.