Nomenclature of Aromatic Compounds
Nomenclature of Benzene Derivatives
Benzene derivatives are isolated from two major sources: petroleum and coal and they are utilized as industrial reagents for over a century. Many of the simple aromatic compounds are traditionally named by their common names and not by their systematic IUPAC names. Some of the widely used ones are summarized in Figure 1.
Unlike aliphatic organic compounds, above mono-substituted benzene derivatives (many others) have names incorporated with substituents. One should memorize these names.
Mono-substituted benzene derivatives (the ones not having common names) are systematically named by naming the substituent first followed by a parent name -benzene.
A compound in which an alkyl group having seven or more carbon atoms is attached to benzene ring is named as phenyl substituted hydrocarbon. The benzene ring is considered as a substituent, and it is named as phenyl.
Similarly, benzyl groups (C6H5-CH2-) are like phenyl groups. The benzyl group is named first followed by the name of substituent in compounds having benzyl group attached to substituents.
Di-substituted benzenes are named systematically by using one of the prefixes ortho (-o), meta (-m), or para (-p). In ortho di-substituted benzene the two substituents are present at 1 and 2 positions of the ring. In meta di-substituted benzene, the two substituents are present at 1 and 3 positions whereas, in para di-substituted benzene, the two substituents are present at 1 and 4 positions. Numbers can also be used in naming substituted benzenes.
Benzene rings containing three or more substituents are named using simple numbering instead of -ortho, -mata, and -para prefixes. In this case the parent name is assigned as a common name if any of the substituent is present on benzene ring listed in Figure 1. The substituent of parent name is numbered as 1. The substituents are numbered such that they get the lowest possible number. Once they are numbered, they are listed in an alphabetical order. If any substituent is present in multiple then the prefixes di-, tri- and tetra- are used accordingly.
The preference order of the functional groups is summarized below.
Following are few examples of naming the parent chain according to preferences shown in table above.
