Triplet-state aromaticity of 4n pi-electron monocycles: Analysis of bifurcation in the pi contribution to the electron localization function
2008 (English)In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 9, no 2, 257-264 p.Article in journal (Refereed) Published
The pi contribution to the electron localization function (ELF) is used to compare 4n pi- and (4n+2)pi-electron annulenes, with particular focus on the aromaticity of 4n pi-electron annulenes in their lowest triplet state. The analysis is performed on the electron density obtained at the level of OLYP density functional theory, as well as at the CCSD and CASSCF ob initio levels. Two criteria for aromaticity of all-carbon annulenes ore set up: the span in the bifurcation values Delta BV(ELE pi) should be small, ideally zero, and the bifurcation value for ring closure of the pi basin RCBV(ELF pi) should be high (>= 0.7). On the basis of these criteria, nearly all 4n pi-electron annulenes are aromatic in their lowest triplet states, similar to (4n+2)pi-electron annulenes in their singlet ground states. For singlet biradical cyclobutadiene and cyclo-octatetraene constrained to D-4h and D-8h symmetry, respectively, the RCBV(ELF pi) at the CASSCF level is lower (0.531 and 0.745) than for benzene (0.853), even though they have equal proportions of alpha- and beta-electrons.
Place, publisher, year, edition, pages
2008. Vol. 9, no 2, 257-264 p.
ab initio calculations, annulenes, aromaticity, density functional calculations, ELF (electron localization function)
IdentifiersURN: urn:nbn:se:uu:diva-112431DOI: 10.1002/cphc.200700540ISI: 000253177700008PubMedID: 18200480OAI: oai:DiVA.org:uu-112431DiVA: diva2:286191