Assessment of σ-diatropicity of the cyclopropane molecule

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