Theoretical determination of the magnetic properties of 2-pyrone and 4-pyrone, and o-benzoquinone and p-benzoquinone

A series of theoretical procedures, relying on the conventional common-origin and distributed-origin approaches, and adopting extended gaugeless as well as London basis sets, have been applied at the Hartree-Fock level of accuracy to predict magnetic susceptibilities and nuclear magnetic shieldings of four molecular systems that aroused particular interest and discussion concerning their aromatic character. The theoretical results are of near Hartree-Fock quality. Comparison with experimental values for magnetic susceptibilities seems to indicate that the latter need to be revised. Analysis of calculated properties and of plots of current density induced by the magnetic field in the pi-electrons provides simple and effective tools for the classification of 2- and 4-pyrones, and o- and p-benzoquinone as non-aromatic.