Discuss the directive influence of substituents on disubstitution in benzene. 

All the six hydrogen atoms of benzene are equivalent. Therefore, replacement of any one of these six hydrogen atoms by any substituent always gives a single monosubstituted benzene derivative. But in the case of disubstitution, three isomeric products are possible. These are ortho (o), meta (m) and para (p).

The position to be occupied by the second entering group depends on upon the nature of the group already present. This ability of a group already present in the benzene ring to direct the incoming group to a particular position is called the directive influence of groups. The groups have been classified into two types:
(i) Ortho and para directing groups: Such groups are directing the incoming group to attack at the ortho and para positions. For example,


In general, all electron donating groups are o, p-directing.
(ii) Meta directing groups. Such groups direct the incoming group to attack at the meta position. For example -NO₂, - CN, -CHO, -COR, -COOH, -SO₃H etc.

In general, all electron withdrawing groups are m-directing.