The shell structure of π ring currents in the expanded porphyrin amethyrin

Abstract

Direct ab initio mapping of induced current density in the π system of the expanded porphyrin amethyrin shows a picture at variance with the conventional 4n π ascription of antiaromaticity. The ipsocentric orbital model interprets the pattern of currents as a superposition of shell contributions: an intense paratropic ring current concentrated on the inner 20-site cycle, counteracted by a weaker diatropic circulation on a 24-site conjugation pathway and a combination of local 5-site diatropic circulations on the six pyrrolic rings.