Question
Why electron withdrawing groups such as - NO2 show their effect only at O and P - position and not at m - position.
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Answer
→ 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.
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