Two molecular species are defined to be isoresonant if each have like numbers of the same (type of) bonds and there is an isomorphism between superpositions of pairs of Kekulé structures giving equivalent interaction patterns (as appear in Hamiltonian matrices). Thus a close physico-chemical correspondence follows, as predicted by a variety of semiempirical quantum-chemical models, and thence presumably for corresponding molecules. Notably simple structural criteria sufficient for isoresonance are found.
