A new electronic theory of pericyclic chemistry and aromaticity, in line with the Robinson/Ingold electronic theory, is proposed. It is referred to as the Cplex-isoelectronic theory. This represents the first successful theory that is not based on quantum mechanics. There are three assumptions in this theory (1) ADEP, (2) SDEP and (3) SDSE. The ADEP assumption refers to isoelectron pairs moving in an antiperiplanar mode in relation to the plane of the molecule. SDEP relates to isoelectron pairs moving in a synperiplanar mode and SDSE refers to single isoelectrons moving in a synperiplanar mode. These assumptions are deduced from nucleophilic, radical addition, S(N)2 and S(N)2' reactions and the anomeric effect. Application of the ADEP concept to pericyclic reactions is supported by Complexity theory and backed up by direct empirical evidence from 1,3-dipolar cycloaddition reactions involving nitronates and by its ability to predict the experimental data. The heavy atom effect provides experimental evidence for the SDSE mode in pericyclic reactions. The HOMO Diels-Alder is consistent with the SDEP concept. Evidence for the assumptions in aromatic compounds is found in the observation of a diamagnetic ring current in the presence of an applied field and in the applicability of the Biot-Savart law. The Cplex-isoelectronic theory makes different predictions from the present quantum chemical methods in some cases, namely the existence of suprafacial concerted thermal [2 + 2], [4 + 4], [6 + 2] and [6 + 6] cycloadditions, suprafacial concerted photochemical [4+2] and [6 +4] cycloadditions, stepwise [2+2+2] cycloadditions of ethyne, diamagnetic ring currents for some cyclic systems with 4n pi electrons. The available empirical evidence is consistent with these predictions. This finding is consistent with Santilli's hadronic chemistry which proposes that the present quantum chemical theories require the addition of a small correction factor for molecules with two or more electrons. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.