A unified orbital model of delocalised and localised currents in monocycles, from annulenes to azabora-heterocycles
Soncini, Alessandro × Domene, C Engelberts, JJ Fowler, PW Rassat, A van Lenthe, JH Havenith, RWA Jenneskens, LW #
Wiley-v c h verlag gmbh
Chemistry - a European Journal vol:11 issue:4 pages:1257-1266
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 electro-negativity parameter, an ipsocentric frontier-orbital model also predicts the transition from delocalised currents in carbocycles to nitrogen-localised currents in alternating azabora-heterocy-cles, 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.