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Issue 2, 2004
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Localisation and reversal of paratropic ring currents in molecules with formal anti-aromatic electron counts

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Abstract

The aromatic character of the six smallest members of the α,ω-bicyclopentadiene-polyacene series (1(n)) has been assessed using magnetic and energetic criteria. Current density maps (CTOCD-DZ/6-31G**//B3LYP/6-31G**) show that, along the series, the ring current changes from paratropic in pentalene (1(0)) and s-indacene (1(1)), through quenched in 1(2) and 1(3), to diatropic in 1(4) and 1(5). These changes are rationalised in terms of orbital contributions to current. Valence bond calculations (VB/6-31G//B3LYP/6-31G**) in which the π system is composed of strictly atomic p-orbitals, show that the electronic structures in these homologous series can be described in terms of the two closed-shell Kekulé resonance structures for the smallest molecules, but that in the larger molecules allyl-polyacene-allyl biradical structures prevail, owing to the larger resonance energies. This trend in electronic structure parallels the switch from paratropic to diatropic character.

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Article information


Submitted
15 Sep 2003
Accepted
06 Oct 2003
First published
23 Oct 2003

Phys. Chem. Chem. Phys., 2004,6, 289-294
Article type
Paper

Localisation and reversal of paratropic ring currents in molecules with formal anti-aromatic electron counts

R. W. A. Havenith, J. J. Engelberts, P. W. Fowler, E. Steiner, J. H. van Lenthe and P. Lazzeretti, Phys. Chem. Chem. Phys., 2004, 6, 289
DOI: 10.1039/B311255A

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