Magnetic resonance energy and aromaticity of polycyclic aromatic hydrocarbon dianions/dications

Molecular dianions/dications of many polycyclic aromatic hydrocarbons (PAHs) have long been regarded as anti-aromatics because of their global paratropic pi-electron current. However, many of them are supposed to be aromatic due to their positive topological resonance energies (TREs). In order to reconcile such energetic and magnetic criteria of aromaticity. we derived a new TRE-like energetic quantity from the magnetic response of the pi-system and called it a magnetic resonance energy (MRE). MIZE was found to be highly correlative with TRE for a variety of PAHs and their molecular dianions/dications. We can now discuss energetic and magnetic criteria of aromaticity unambiguously on this theoretical basis. Many PAH dianions/dications indeed turned out to be aromatic with positive MREs even if they exhibit paratropic Currents along the periphery of the pi-system.