Chemical Physics Letters vol:401 issue:1-3 pages:164-169
Shielding-density functions interpret nuclear magnetic shieldings point-wise, through the Biot-Savart law. For aromatic, anti-aromatic, and non-aromatic pi-systems (benzene, cyclooctatetraene, borazine), the characteristic pattern of current density leads to a distinctive map for the pi-contribution to the perpendicular components of H-1 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 pi-current produces an intense deshielding ipso spike, weakly cancelled by a remote shielding ridge; paratropic anti-aromatic pi-current inverts these features; localised pi-currents produce cancelling shielding/deshielding spikes. Ring-currents also contribute characteristically to out-of-plane carbon shieldings. (C) 2004 Elsevier B.V. All rights reserved.