Substituent effects in Friedel-Crafts reactions

The reactivity of aromatic pi bonds in S_EAr reactions is very sensitive to the presence of electron-donating groups (EDG) and electron-withdrawing groups (EWG) on the aromatic ring.  This is due to the carbocation nature of the intermediate, which is stabilized by electron-donating groups and destabilized by electron-withdrawing groups.  As a rule, both the acylation and alkylation Friedel-Crafts reactions fail when meta-directing deactivators are present. Thus nitrobenzene (a deactivated ring) fails to react in the Friedel-Crafts reaction. However the reaction is successful with halogen substituents are present, as in chlorobenzene.

The Friedel-Crafts alkylation of methoxy benzene would be expected to produce a mixture of the ortho and para substituted products, but no meta-substituted product.

In addition, the para product would be expected to be preferred over the ortho product, due to steric and inductive considerations.