Monosubstituted benzenes are named using the substituent followed by benzene without a number to indicate position. Disubstituted benzenes can be named with ortho, meta, and para or numbers. Polysubstituted benzenes must use numbers for location.
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 () 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.