Aromaticity Changes along the Lowest-Triplet-State Path for C=C Bond Rotation of Annulenyl-Substituted Olefins Probed by the Electron Localization Function
2009 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 113, no 44, 12304-12310 p.Article in journal (Refereed) Published
The pi-contribution to the electron localization function (ELF pi) was used to analyze changes in the aromaticity of annulenyl-substituted olefins in their lowest triplet state (T-1) when the structure around the olefin C=C bond is twisted from planar to a structure ((3)p*) at which the planes of the two RR'C units are perpendicular The ring closure bifurcation value and the range in the bifurcation values of the ELF pi basins serve as (anti)aromaticity indicators directly linked to the electronic structure. Both Huckel's 4n + 2 pi-electron rule for aromaticity in the singlet ground state (S-0) and Baird's 4n pi-electron rule for aromaticity in the lowest pi pi* triplet state are applied. Three olefins with S-0 aromatic (T-1 antiaromatic) substituents and four olefins with T-1 aromatic (So antiaromatic) substituents were studied using the ELF pi topology at the OLYP/6-311G(d,p) density functional theory level The changes in the substituent ELF pi. bifurcation values upon rotation about the olefin bond in the T-1 state reveal that aromatic character is recovered for the first three olefins and that it is reduced for the latter ones. These changes in aromatic character are reflected in the shapes of the T-1 potential energy surfaces as a twist away from planar structures in olefins with T-1 antiaromatic substituents is energetically favorable, but that in olefins with T-1 aromatic substituents is unfavorable. Hence, aromaticity change is a driver for a photochemical reaction as for many ground-state reactions
Place, publisher, year, edition, pages
2009. Vol. 113, no 44, 12304-12310 p.
IdentifiersURN: urn:nbn:se:uu:diva-127453DOI: 10.1021/jp904335jISI: 000271105800032PubMedID: 19799456OAI: oai:DiVA.org:uu-127453DiVA: diva2:330092