The concept of aromaticity is examined in terms of a delocalised ring current contribution to the proton NMR shielding of ferrocene and related compounds. The source of the ring current is derived as a delocalised contribution to the experimentally determined chemical shift, where the local contribution is calculated from predictions based on the experimental 13C shielding tensors. Examined are dibenzenechromium, ruthenocene, benzene, hexamethylbenzene and several derivatives of ferrocene with attention to: (i) the effects of complexation of the benzene ring, (ii) the protons in an aliphatic bridge on a ferrocene cyclopentadienyl ring, and (iii) the electric field effects of the permanent electric dipole moment in pentamethylferrocene.
