[confusedcollegestudent]

My professor said that if there is already a meta director or a strong EDG, there won't be a reaction.
She gave us an example, m-phthalic acid, which she says does not undergo any reaction if it reacts with CH₃Cl and AlCl₃
However, there was a problem, p-nitrobenzoic acid undergoing a chlorination even though it has two EDG like the m-phthalic acid does.
Why is this? Is this because the two groups are different on the nitrobenzoic acid and the phthalic acid aren't?

[kriggy]

The difference is that one reaction is FC alkylation and the other is halogenation. You cant compare those two directly.
Also, I dont realy see a reasong why strong EDG would stop the FC alkylation when the reaction is S_EAr which gets promoted by electron donating groups, didnt she mean EWG? It seems you have the terms confused: EDG = electron donating group (increases electron density on the aromatic ring), EWG= electron withdrawing group (decreases electron density on the aromatic ring)