Directive Influence of Functional Groups
In case of substituted aromatic compounds, the functional groups already present directs the next incoming group to a particular position in the aromatic ring. It is called directive influence of the group already attached to the benzene ring.
Chlorination of Phenol
For example, phenol on chlorination gives a mixture of ortho-chlorophenol and para-chlorophenol as –OH groups is an ortho and para directing group.
Chlorination of Nitrobenzene
In case of nitrobenzene, –NO2 group is a meta directing group and hence, the product obtained on chlorination is meta-chloronitrobenzene.