Nucleus-independent chemical shifts from semiempirical calculations

A recently developed special MNDO parameterization for NMR chemical shifts is used to compute the nucleus-independent chemical shifts (NICS) for a wid e range of organic molecules, including [n]annulenes, polycyclic hydrocarbo ns, heterocycles, cage molecules, fullerenes, and pericyclic transition sta tes. The results are compared with published NICS data from ab initio and d ensity functional calculations. In general, there is reasonable agreement. The semiempirical NICS values tend to be smaller in absolute value than the ir ab initio counterparts, but they often show similar trends. The aromatic or antiaromatic character of a given system can normally be assigned corre ctly on the basis of the MNDO NICS values.