Ring-current signatures in shielding-density maps

Shielding-density functions interpret nuclear magnetic shieldings point-wise, through the Biot–Savart law. For aromatic, anti-aromatic, and non-aromatic π-systems (benzene, cyclooctatetraene, borazine), the characteristic pattern of current density leads to a distinctive map for the π-contribution to the perpendicular components of 1H shielding-density. Hence, global and localised currents have distinguishable signatures, dependent on separation between outward and return circulations in the current–density map. Aromatic, diatropic π-current produces an intense deshielding ipso spike, weakly cancelled by a remote shielding ridge; paratropic anti-aromatic π-current inverts these features; localised π-currents produce cancelling shielding/deshielding spikes. Ring-currents also contribute characteristically to out-of-plane carbon shieldings.