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 .