Covalent and non covalent complexes between aromatic carbocyclic and heterocyclic nucleophilic and electrophilic reagents

Both electrophilic and nucleophilic aromatic substitution reactions proceed through a multistep pathway. The observation of separate steps and the characterization of non-covalent and covalent complexes is strongly dependent on the nature of starting materials, belonging to both, heterocyclic and carbocyclic aromatic series, and on the experimental conditions with particular attention to solvent. For reactions carried out between superelectrophilic and supernucleophilic reagents, a new class of  complexes, contemporaneously Wheland and Meisenheimer complexes, has been isolated and characterized