Nomenclature of Benzene and Aromatic Compounds

Benzene is the accepted name for C₆H₆ by the International Union of Pure and Applied Chemistry (IUPAC). The derivatives of benzene are a large group of useful chemical compounds. A derivative is a compound that is derived from a similar compound by a chemical reaction. Many of the derivatives of benzene contain just a single functional group attached to the benzene ring and are named by adding the prefix of the substituent group to the word benzene. For example, nitrobenzene (C₆H₅NO₂) is a compound with a nitro (${-}{\rm{NO}}_2$) group attached to a benzene ring. There are a number of common benzene derivatives that also have non-IUPAC names. A derivative of benzene with only one substituent is referred to as a monosubstituted derivative. Examples of common, monosubstituted benzenes that are often referred to by non-IUPAC names include anisole (methoxybenzene, C₆H₅OCH₃), aniline (aminobenzene, C₆H₅NH₂), and toluene (methylbenzene, C₆H₅CH₃). A derivative of benzene with two substituents is referred to as a disubstituted derivative. Some of these, such as xylene (C₈H₁₀), have non-IUPAC names. For disubstituted benzene derivatives, ortho, meta, and para are used to indicate the position of the substituents. Ortho (abbreviated o-) is a prefix that indicates there are no carbon atoms between the carbon atoms that have the substituents, producing a 1,2-disubstituted benzene pattern. Meta (abbreviated m-) is a prefix that indicates there is one carbon atom between the carbon atoms that have the substituents, producing a 1,3-disubstituted benzene pattern. Para (abbreviated p-) is a prefix that indicates there are two carbon atoms between the carbon atoms that have the substituents, producing a 1,4-disubstituted benzene pattern. Thus, 1,2-dimethylbenzene is also called ortho-xylene or o-xylene, 1,3-dimethylbenzene is meta-xylene or m-xylene, and 1,4-dimethylbenzene is para-xylene or p-xylene. A benzene with more than two substituents is referred to as a polysubstituted derivative. When naming these, the highest-priority substituent is numbered as 1, and numbering continues around the ring so as to give the other substituents the lowest combination of numbers.