フリーデル・クラフツ反応

抄録

Friedel-Crafts reactions are the electorophilic reactions catalyzed by Lewis acid type acidic halides or proton acids. They require a reactant-catalyst complex which can interact with either π-or δ-donor type subutrates.The electrophilic complex is either polarized or ionic type. There is no difference in principle between reactions of π- and δ-donor systems, but the π-bonds generally react more readily. Reaction of the electorophilic complex with the substrate results in the formation of an intermediate δ-complex, which determines the reaction rate. Electrophilic aromatic substitutions involving strongly electrophilic reagents show low substrate selectivity, but high positional selectivity. This suggests that the transition state lies early on the reaction coordinate, resembling π-complex. In reactions with weak electrophiles, it lies late, resembling intermediate δ-complex.