[lugerard]

Can anyone tell me why friedel crafts alkylation do not permit a meta director reaction on a benzene ring with a NO2 substituent? It is said that NO2 withdraws electrons hence direct incoming groups to the meta position but not for friedel crafts.

[Jorriss]

I can't say with certainty but have you tried drawing the resonance structures for all the possible combinations? I'd suspect if this is done it turns out they're are more, or more stable ones, for the other positions.

Sorry it's not the most helpful response.

[bolo]

The benzene ring with nitro group as a substituent is too less nucleophilic for F-C reaction.

[Rishi]

I presume that the Fridel-Caraft alkylation needs an electron rich position as the attacking group is R-CO+. Now since the presence of NO2 group makes the meta position more susceptible for electron withdrawl, the meta becomes electron deficient to readily accept the RCO+.

[pacifyer]

The aromatic ring must be at least as nucleophilic as benzene for Friedel-Crafts alkylations to occur. In deactivated rings, it will fail.