3. Ortho and para directing groups and deactivating- Halogens because of their strong – I effect, overall electron density on benzene ring decreases. However, due to resonance the electron density on o – and p – positions is greater than that at the m-position. Hence, they are also o – and p – directing groups.
CARCINOGENICITY AND TOXICITY-
Benzene and polynuclear hydrocarbons containing more than two benzene rings fused together are toxic and said to possess cancer producing( carcinogenic) property.