Aromatic Conjugation Pathways in Porphyrins
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The π-current density induced in a polycyclic π-system is strongly dependent on molecular geometry, so that information on main aromatic pathways cannot be extracted straightforwardly from the π-current density. Using our graph theory of aromaticity and ring-current diamagnetism, we re-interpreted the π-current densities and aromatic stabilization energies of porphyrins consistently and found that main pathways of π-electron circulation along the macroscopic ring are not those of aromatic stabilization. Four five-site circuits instead proved to be the main origin of aromaticity in porphyrins. In general, currents are induced in all possible circuits in a π-system. Superposition of all these circuit currents gives rise to the apparent bifurcation of the π-current across each pyrrolic unit. Local π-currents induced in pyrrolic rings represent those induced in the corresponding five-site circuits.
- Bull. Chem. Soc. Jpn.
Bull. Chem. Soc. Jpn. 81(7), 826-835, 2008-07-15
The Chemical Society of Japan