As shown, the presence of nitro group at ortho- and para-positions withdraws the
electron density from the benzene ring and thus facilitates the attack of the nucleophile
on haloarene The carbanion thus formed is stabilised through resonance The negative
charge appeared at ortho- and para- positions with respect to the halogen substituent is
stabilised by –NO2 group while in case of meta-nitrobenzene, none of the resonating
structures bear the negative charge on carbon atom bearing the –NO2 group Therefore,
the presence of nitro group at meta- position does not stabilise the negative charge and
no effect on reactivity is observed by the presence of –NO2 group at meta-position