Key Idea : Deactivating groups attached on benzene ring are meta-directing groups. The product formed in the given reaction is
In the above reaction, ' N′ bears a positive charge that decreases the electron density due to its strong − I effect and hence is called a deactivating group. The overall electron density on the benzene ring decreases (inspite of three −CH3 groups) thus, the electrophilic substitution becomes difficult. The electron density on 0 -and p -position is comparatively lesser than that at m -position. So, electrophile attacks at m -position i.e. substitution occur at m -position.