Question

chlorination of nitrobenzene is difficult as compared to nitration of chlorobenzene. explain​

Answer 1

Explanation:

Aromatic nitration is a kind of electrophilic aromatic substitution. Its rate depends on how electron-rich the ring is; more electron-rich rings react faster. (Nucleophilic aromatic substitution, by the way, is the opposite; electron-poor rings are the most activated toward such reactions.) Since chloro is an electron-withdrawing substituent, chlorobenzene is less electron-rich than benzene. Therefore the nitration will be slower.

Answer 2

Explanation:

All of the halogens (F,Cl,Br,I) are more electronegative than hydrogen. Therefore they will inductively remove electron density from a benzene ring. However, you can also draw resonance structures for the various halobenzenes where the halogen substituent is donating electron density to the ortho and para positions of the benzene ring through resonance.

Therefore, in the case of the halobenzenes these two effects are working in opposite directions.