A criterion to demarcate the dual Diels–Alder and σ-complex behaviour of aromatic and heteroaromatic superelectrophiles

A frontier demarcating superelectrophilic compounds that undergo both Diels–Alder reactivity and σ-complexation reactions, from traditional electrophiles, is afforded through the thermodynamic tendency for σ-complexation as defined by the pKa values for H2O addition to electron-deficient aromatic and heteroaromatic substrates.