Theoretical studies on the benzene molecule. II. Criticism of the ring current model.

The pattern of the electron currents, induced in the benzene molecule by uniform magnetic fields, has been visualized by plotting modulus and direction of the quantum mechanical current density vector evaluated within the coupled Hartree–Fock approximation assuming a basis set of 198 CGTOs. The electron motion is characterized by axial and toroidal vortices and the paramagnetic sigma circulation overcomes the diamagnetic pi ring current. Intense localized circulations occur about carbon nuclei and carbon–carbon bonds, which give rise to important deshielding effects upon protons. The delocalized currents are most intense in the environment of carbons; delocalized currents are also present, and no actual ''superconductivity'' of pi electrons can be accounted for. The reported results document that London's ring current is a rough oversimplification, affected by some unnecessary and unphysical hypotheses.