Arrange the following set of compounds in the order of their decreasing relative reactivity with on electrophile . Give reason .

Explanation

The reactivity of arenes towards electrophiles depends upon their relative electron density in the benzene ring . Higher the electron density , more reactive is the arene. Now `OCH_3` group in anisole is strongly electron donating due to its +R-effect. As a result , it increases the electron density in the ring and hence makes anisole more reactive than benzene towards electrophiles

On the other hand, `-NO_2` group in nitrobenzene and Cl atom in chlorobenzene , both are electron-withdrawing and hence decrease the electron density in the ring. As a result, both nitrobenzene and chlorobenzene are less reactive than benzene towards electrophiles. But `-NO_2` group is a strong electron-withdrawing group due to its strong -R effect and strong -I-effect. In contrast, Cl atom is only a weak electron-withdrawing group due to its only weak -I- effect. In other words, electron density in chlorobenzene is more than in nitrobenzene and hence chlorobenzene is more reactive than nitrobenzene towards electrophiles . Thus, the overall reactivity of these three compounds towards electrophiles decreases in the order :
anisole gt chlorobenzene gt nitrobenzene .