title: A unified orbital model of delocalised and localised currents in monocycles, from annulenes to azabora-heterocycles.
abstract: Why are some (4n+2)pi systems aromatic, and some not? The ipsocentric approach to the calculation of the current density induced in a molecule by an external magnetic field predicts a four-electron diatropic (aromatic) ring current for (4n+2)pi carbocycles and a two-electron paratropic (antiaromatic) current for (4n)pi carbocycles. With the inclusion of an electronegativity parameter, an ipsocentric frontier-orbital model also predicts the transition from delocalised currents in carbocycles to nitrogen-localised currents in alternating azabora-heterocycles, which rationalises the differences in (magnetic) aromaticity between these isoelectronic pi-conjugated systems. Ab initio valence-bond calculations confirm the localisation predicted by the naive model, and coupled-Hartree-Fock calculations give current-density maps that exhibit the predicted delocalised-to-localised/carbocycle-heterocycle transition.
authors.affiliation: Department of Chemistry, University of Exeter, Stocker Road, Exeter EX4 4QD, UK.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Soncini
authors.forename: Carmen
authors.initials: C
authors.lastname: Domene
authors.forename: Jeroen J
authors.initials: JJ
authors.lastname: Engelberts
authors.forename: Patrick W
authors.initials: PW
authors.lastname: Fowler
authors.forename: André
authors.initials: A
authors.lastname: Rassat
authors.forename: Joop H
authors.initials: JH
authors.lastname: van Lenthe
authors.forename: Remco W A
authors.initials: RW
authors.lastname: Havenith
authors.forename: Leonardus W
authors.initials: LW
authors.lastname: Jenneskens