Professor Amnon Stanger sent me an email with a couple of comments concerning points made in my book. I take up the first of his comments here. Stanger has pointed me to what looks to be the true first study evaluating NICS on a grid of points, done by Klod and Kleinpeter in 2001.¹ They computed NICS values on a 3-D grid and then created iso-chemical-shielding surfaces to pictorially represent the shielding and deshielding zones (or cones) created by π-bonds (like ethane and ethyne) and aromatic compounds. In a similar vein, Lazzeretti² evaluated the out-of-plane component of the magnetic shielding tensor (σ_||) on a 2-D grid to demonstrate the shielding and deshielding zones of π-systems, particularly aromatic systems. These plots clearly demonstrate the “cones” one typically finds in introductory organic texts to explain NMR effects.

(1) Klod, S.; Kleinpeter, E., “Ab Initio Calculation of the Anisotropy Effect of Multiple Bonds and the Ring Current Effect of Arenes—Application in Conformational and Configurational Analysis,” Chem. Soc., Perkin Trans. 2, 2001, 1893-1898, DOI: 0.1039/b009809o.

(1) Viglione, R. G.; Zanasi, R.; Lazzeretti, P., “Are Ring Currents Still Useful to Rationalize the Benzene Proton Magnetic Shielding?,” Org. Lett., 2004, 6, 2265-2267, DOI: 10.1021/ol049200w.