Side chain - nomenclature of simple aromatic compounds

The alkyl or any other aliphatic group consisting of at least one carbon atom attached to the nucleus is termed as side chain. These are made by replacing one or more hydrogen atoms in the ring by alkyl radicals that is R (R may be -CH₃,-C₂H₅,-C₃H₇ etc.)

If one atom of hydrogen of benzene molecule is changed by other atom or group of atoms, the derivative formed is known as monovalent substituted derivative. It can present only in one form since all the six hydrogens of benzene denote equivalent positions. For instance, C₆H₅X, in which X is a monovalent group.

While two hydrogen atoms of benzene are replaced by two monovalent atoms or group of atoms, the resultant product disubstituted benzene derivative can have three different types of forms. These forms are differentiated by giving the numbers. The position occupied by the principle functional group is given like 1 and the other position is numbered in a clockwise direction that gives lower locatant to the substituents.