Aromaticity and Diatropicity

Aromaticity can be interpreted as extra stabilization of a cyclic unsaturated molecule arising from cyclic conjugation of mr-electrons. The extra stabilization energy is estimated relative to the r-electron energy of a hypothetical reference molecule formed by the "localized" ir bonds. It is termed the resonance energy due to aromaticity. Our graph theory of aromaticity defines this type of resonance energy exactly. Diamagnetic susceptibility due to ring currents can be formulated in the same graph-theoretical terms. This formula reveals that aromatic stabilization and diamagnetic susceptibility exaltation arise from the same cyclic interactions of v electrons. For conjugated systems, both monocyclic and polycyclic, the susceptibility due to a ring current induced in any of the Tc-electron rings is roughly proportional to the contribution of the ring to the resonance energy, multiplied by a factor proportional to the ring area squared.