By partitioning the bond current strength (current susceptibility) into plane symmetric and plane antisymmetric contributions, it is shown that 91% of the diatropic ring current of benzene is transported by the π electrons and the remaining non-negligible 9% is sustained by the σ electrons. In planar cyclooctatetraene 94% (6%) of the paratropic ring current is transported by the π (σ) electrons. In cyclopropane 95% (5%) of the diatropic ring current is transported by the σ (π-like) electrons. The 85% fraction of the diatropic ring current of Al4(2-) is transported by the σ valence electrons and 15% by the π valence electrons. In the nonaromatic borazine system the nitrogen-centered π electron circulations are surrounded by a weak diatropic "ring current" 6.5 times smaller than that of benzene.

Spatial models of the current density field induced in the cyclopropane molecule by stationary, homogeneous magnetic fields, parallel to either the C3 or the C2 symmetry axis, have been constructed. A compact, abridged representation of the models is given via stagnation graphs that convey essential information. Maps of streamlines and moduli are also reported to complete current models that have proven useful to rationalize magnetic tensor properties, that is, magnetizability, 1H and 13C nuclear shieldings, and magnetic shielding along the C3 symmetry axis. Plots of Biot-Savart magnetic shielding density combined with current density visualization yield an accurate, detailed account of the shielding mechanisms. The magnetropicity of the system described by the current density model is fully consistent with the magnitude of magnetic tensors calculated at near Hartree-Fock level. In a field perpendicular to the molecular plane, cyclopropane sustains a diatropic sigma-ring current with the following peculiar features: (i) it follows the molecular periphery rather than the CC framework; (ii) it bifurcates in the proximity of the methylene moieties flowing along the CH bonds, both above and below the sigma(h) plane; (iii) it has an effect on the values of response properties, although it is not as large as expected from naive arguments (e.g., the center-of-mass value of the magnetic shielding constant is dominated by in-plane components rather than the out-of-plane component, which is in contrast to pi-aromatic systems such as benzene); (iv) it has a negligible effect on the strong anisotropy of carbon magnetic shielding, which is shown to arise from local currents. No evidence for strong diatropism, and therefore sigma-aromaticity of the cyclopropane molecule, was found on the magnetic criterion.

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