Electrophilic and Nucleophilic Aromatic Substitutions are Mechanistically Similar with Opposite Polarity.

Confrontation of the recently formulated general mechanism of nucleophilic substitution in electron-deficient arenes with the well-known mechanism of electrophilic substitution revealed that these fundamental processes are mechanistically identical but proceed according to opposite polarity-an Umpolung relation. In this viewpoint this apparently controversial concept is supported by discussion of a variety of experimental results.