A unified orbital model of delocalised and localised currents in monocycles, from annulenes to azabora-heterocycles

Alessandro Soncini, Carmen Domene Nunez, Jeroen J Engelberts, Patrick W. Fowler, André Rassat, Joop H van Lenthe, Remco W. A. Havenith, Leonardus W. Jenneskens

Research output: Contribution to journalArticlepeer-review

48 Citations (Scopus)

Abstract

Why are some (4n+2)π 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)π carbocycles and a two-electron paratropic (antiaromatic) current for (4n)π 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 π-conjugated systems. Ab initio valence-bond calculations confirm the localisation predicted by the naïve model, and coupled-Hartree–Fock calculations give current-density maps that exhibit the predicted delocalised-to-localised/carbocycle–heterocycle transition.
Original languageEnglish
Pages (from-to)1257-1266
Number of pages10
JournalChemistry - A European Journal
Volume11
Issue number4
DOIs
Publication statusPublished - 1 Feb 2005

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