Substituent effect:

Of the three possible isomers taking place from the bromination of toluene, just two (the ortho and para) are created in significant quantity. Additionally, the bromination of toluene goes at a faster rate as compared to the bromination of benzene. Why? The reply lies in the fact that the methyl substituent can influence the rate and the position of further substitution. A substituent can either activate or deactivate the aromatic ring in the direction of electrophilic substitution and does so by the inductive or resonance effects. A substituent can as well direct the next substitution so that it goes chiefly ortho/para or mainly Meta.

We can categorize substituents into four groups depending upon the effect they have on the rate and the position of substitution, that is:

• Activating groups that direct ortho/para through inductive effects;
• Deactivating groups that direct meta through inductive effects;
• Activating groups that direct ortho/para through resonance effects;
• Deactivating groups that direct ortho/para through resonance effects.

There are no substituents that activate the ring and direct Meta.