Theoretical Studies on Graphyne Substructures:  Geometry, Aromaticity, and Electronic Properties of the Multiply Fused Dehydrobenzo[12]annulenes

The geometries of multiply fused dehydrobenzo[12]annulenes [12]DBAs 2−7 with various topologies, which are considered as graphyne fragments, have been optimized at the B3LYP/6-31G* level of theory. Most of the optimized geometries of fused DBAs have planar structures excluding a boomerang-shaped bis...

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Bibliographic Details
Published in:Journal of organic chemistry 2007-02, Vol.72 (4), p.1437-1442
Main Authors: Tahara, Kazukuni, Yoshimura, Takashi, Sonoda, Motohiro, Tobe, Yoshito, Williams, Richard Vaughan
Format: Article
Language:English
Subjects:
Alicyclic compounds
Alicyclic compounds, terpenoids, prostaglandins, steroids
Chemistry
Exact sciences and technology
Organic chemistry
Preparations and properties
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Summary:The geometries of multiply fused dehydrobenzo[12]annulenes [12]DBAs 2−7 with various topologies, which are considered as graphyne fragments, have been optimized at the B3LYP/6-31G* level of theory. Most of the optimized geometries of fused DBAs have planar structures excluding a boomerang-shaped bisDBA 4, a trefoil-shaped trisDBA 6, and a wheel-shaped DBA 7. For the boomerang-shaped bisDBA 4 and the trefoil-shaped trisDBA 6, distortions originate from the steric repulsion between hydrogen atoms attached to adjacent benzene rings. The harmonic oscillator model of aromaticity (HOMA) values at the central benzene ring of multiply fused DBAs decrease as the number of fused 12-membered rings increases except for the closely related structures 4 and 5 and 6 and 7, because of bond length elongation due to conjugation with the phenylethynyl groups. Nucleus-independent chemical shifts (NICS) were computed at the individual ring centers of the fused DBAs. The fusion of the antiaromatic 12-membered rings results in increasing (more positive) NICS values at the central benzene ring, indicating the decrease of diatropic ring currents. Furthermore, HOMO-LUMO gaps of the DBAs 2−7 are strongly influenced by the molecular topology. The para-conjugation pathway of the bis(phenylethynyl)benzene unit plays a more important role in the determination of the electronic properties of multiply fused DBAs than the meta- and ortho-conjugation pathways.
ISSN:0022-3263
1520-6904
DOI:10.1021/jo0622781