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

The components of nucleus-independent chemical shift (NICS) tensors for D-nh n-annulenes are discussed as indexes of the aromatic character of electronic pi 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 pi system of the ring. Isotropic NICS values at ring centres contain large influences from the sigma 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 pi system, characterizes NICS well.