Graph-Theoretical Re-interpretation of NICS Values for Polycyclic Aromatic Hydrocarbons: Naphthalene and Azulene

Even for the simplest polycyclic aromatic hydrocarbons, such as naphthalene and azulene, the nucleus-independent chemical shift (NICS) calculated at a ring center does not always represent local aromaticity. NICS reflects currents induced in many cyclic paths in a (pi)-system.