title: Macrocyclic conjugation pathways in porphyrins.
abstract: Macrocyclic aromaticity is the most important concept in porphyrinoid chemistry. Bond resonance energy (BRE) for any pi-bond linking adjacent pyrrolic or other rings represents the stabilization energy due to macrocyclic aromaticity. We found that a main conjugation pathway associated with macrocyclic aromaticity can be traced by choosing a pi-bond with a larger BRE at every bifurcation of the pi-network. All pi-bonds located along the main conjugation pathway are intensified with large positive BREs compared with those located along the bypasses. On the other hand, a main destabilization pathway associated with macrocyclic antiaromaticity can be traced by choosing a pi-bond with a smaller BRE at every bifurcation of the pi-network. Macrocyclic conjugation pathways thus determined are fully consistent with the chemical shifts of protons attached to the macrocycle.
authors.affiliation: Department of Chemistry, Faculty of Science, Shizuoka University, Oya, Shizuoka 422-8529, Japan.
authors.forename: Jun-ichi
authors.initials: J
authors.lastname: Aihara