The observation, or the isolation (when it is possible), of intermediates in nucleophilic aromatic substitution [1a](SNAr; the so-called Meisenheimer complexes M) and in electrophilic aromatic substitution [1b, c](the so-called Wheland complexes W) reactions is an important confirmation of the proposed mechanisms. Our interest has, in the past, focused on intermediates in the SNAr reaction [2] and, more recently, also on electrophilic ...
