Aromatic conjugation pathways in porphyrins

The pi-current density induced in,I polycyclic pi-system is strongly dependent oil molecular geometry, so that information oil main aromatic pathways cannot be extracted straightforwardly from the pi-current density. Using our graph theory of aromaticity and ring-current diamagnetism, we re-interpreted the pi-current densities and aromatic stabilization energies of porphyrins consistently and found that main pathways of pi-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 ill a pi-system. Superposition of all these circuit Currents gives rise to the apparent bifurcation of the pi-current across each pyrrolic unit. Local pi-currents induced in pyrrolic rings represent those induced in the corresponding live-site circuits.