The electron density vs. NICS scan: a new approach to assess aromaticity in molecules with different ring sizes.

The influence of electron density on the magnitude of non-nuclear magnetic shielding, NICS, is studied in detail by scanning the electron density vs. NICS(zz) (the out-of-plane component of NICS). This study sheds new light on the role of electron density on the magnitude of NICS. Scanning the electron density vs. NICS(zz) not only helps to discriminate the electronic ring currents operative in aromatic, nonaromatic and antiaromatic species, but also yields a measure to compare the strength of diatropic/paratropic currents in molecules with different ring sizes or different number of π electrons without relying on the methods of σ-π separation.