Question

Explain the directive influence of nitro group in nitrobenzene. 

OR 

Explain why nitro group is a meta-directing group.

Answer 1

i. Meta directing group withdraws electrons from the aromatic ring by resonance, making the ring electron-deficient. Therefore, meta groups are ring deactivating groups.

ii. Due to -I effect, -NO₂ group reduces electron density in benzene ring on ortho and para positions. So, the attack of incoming group becomes difficult at ortho and para positions. The incoming group can attack on meta positions more easily.

 iii. The various resonance structures of nitrobenzene are as shown below:

iv. It is clear from the above resonance structures that the ortho and para positions have comparatively less electron density than at meta positions. Hence, the incoming group/electrophile attacks on meta positions.

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Answer 2

In nitro benzene nitro group, the electron density decreases at ortho and a Para position, thus the incoming electrophile is directed to the Meta position. Ring deactivating groups include –CN, –CHO, –COR, –COOH, –COOR and –SO3H directs the incoming group to Meta position.

NO2 group is an electron withdrawing group. As a result, the electron density at meta position is relatively higher than at the ortho and para position. So, electron deficient electrophile always attacks at meta position. HENCE, nitro group is meta directing in electrophilic aromatic substitution reaction