Ring current model of the naphthalene molecule

Computational methods based on continuous transformation of the origin of current densitieshave been employed at the coupled Hartree-Fock level of accuracy to calculate magneticsusceptibility and carbon and hydrogen nuclear magnetic shielding in the naphthalene molecule.Different schemes based on formal annihilation of the conventional expressions for eitherdiamagnetic or paramagnetic contributions to the current density have been tested. The firstthree-dimensional model for circulation of both s and p electrons in naphthalene is presentedvia diagrams showing streamlines, stagnation lines and modulus of the current density inducedby a magnetic field perpendicular to the molecular plane. The new topological model outlinedin the present work provides a significant step forward with respect to previous findings, usefulin rationalizing the magnetic properties of the naphthalene molecule. The theoretical valuesof proton magnetic shielding indicate that the chemical shift observed experimentally betweenmagnetically non-equivalent hydrogens is entirely due to deshielding of the out-of-planecomponent of sigma H.