Relative weights of σ and π ring currents in a few simple monocycles

By partitioning the bond current strength (current susceptibility) into plane symmetricand plane antisymmetric contributions, it is shown that 91% of the diatropic ring current ofbenzene is transported by the π electrons and the remaining non-negligible 9% is sustained bythe σ electrons. In planar cyclooctatetraene 94% (6%) of the paratropic ring current is transportedby the π (σ) electrons. In cyclopropane 95% (5%) of the diatropic ring current is transported bythe σ (π-like) electrons. The 85% fraction of the diatropic ring current of Al42- is transported bythe σ valence electrons and 15% by the π valence electrons. In the nonaromatic borazine systemthe nitrogen-centered π electron circulations are surrounded by a weak diatropic “ring current”6.5 times smaller than that of benzene.