Induced magnetic fields in aromatic [n]-annulenes—interpretation of NICS tensor components

The components of nucleus-independent chemical shift (NICS) tensors for Dnhn-annulenes are discussed as indexes of the aromatic character of electronic π systems. The component corresponding to the principal axis perpendicular to the ring plane, NICSzz, is found to be a good measure for the characterisation of the π system of the ring. Isotropic NICS values at ring centres contain large influences from the σ system and from all three principal components of the NICS tensor. At large distances away from the ring center, NICSzz, which is dominated by contributions from the π system, characterizes NICS well.