Abstract

It is shown that computed off-nucleus isotropic magnetic shielding isosurfaces and contour plots provide a feature-rich picture of aromaticity and chemical bonding in ground and excited molecular electronic states, which is both quantitative and easy-to-visualise and interpret. These isosurfaces and contour plots make good chemical sense as at atomic positions they are pinned to the nuclear shieldings which, for electronic ground states, are experimentally measurable through chemical shifts. The examples discussed include ground and excited-state aromaticity and antiaromaticity in benzene, cyclobutadiene, cyclooctatetraene and Möbius conjugated rings, the contest between aromaticity and antiaromaticity in norcorrole, the smallest cyclic tetrapyrrole porphyrin analogue synthesized so far, and modern shielding-based visual interpretations of Clar's aromatic sextet theory, heteroaromaticity and multiple carbon-carbon bonds.

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