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, NICS[zz], 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 [omicron] system and from all three principal components of the NICS tensor. At large distances away from the ring center, NICS[zz], which is dominated by contributions from the [pi] system, characterizes NICS well