Question

The presence of electron withdrawing group like -NO2 at ortho- and para- positions increase the reactivity of haloarenes but their presence at meta- positions decrese the reactivity. Justify the statement.

Answer 1

here you can apply the concept of resonance that is you have to remember the fact that the ortho and para positions participate in the shifting of pi bond but the meta position cannot participate in the electron shifting.(i don't have phone so for reference, you can see the diagram of resonance in benzene and you will find that ortho and para will get -ve charge but meta will get +ve charge ) this is why meta does not participate in the resonance