Interpreting the behavior of the NICSzz by resolving in orbitals, sign, and positions

The zz component of the nucleus independent chemical shift or the NICSzz is commonly used as a quantifier of the (anti)aromatic character of a (sub)system. One of the underlying assumptions is that a position can be found where the "aromatic" ring currents are adequately reflected in the corresponding NICSzz value. However, as the NICSzz is the result of an integration over the entire space, it no longer explicitly contains the information needed to quantify the separate contributions arising from underlying current density patterns. In this study, we will show that these contributions can be revealed by resolving the NICSzz into orbitals, sign, and positions. Our analysis of benzene in terms of these resolutions shows that the same underlying current density can lead to highly complex shielding patterns that vary greatly depending on the position of the NICSzz-probe. As such, our results indicate that any analysis solely based on NICSzz-values can lead to results that are difficult to interpret, even if the system under study is considered to be well-known. © 2017 Wiley Periodicals, Inc.