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Paper | Special issue | Vol 79, No. 1, 2009, pp.451-470
Published online, 3rd July, 2008
DOI: 10.3987/COM-08-S(D)1
Out-of-plane Deformation of the Azulene Ring along Its Short Molecular Axis in Crystal and Theoretical Structures of 1,3-Diheterolyl- and 1,3-Diphenylazulenes

Akira Ohta, Shigeyasu Kuroda,* Nguyen Chung Thana, Kouhei Terasawa, Kunihide Fujimori, Keita Nakajima, and Mitsunori Oda*

*bDepartment of Applied Chemistry, Faculty of Engineering, University of Toyama, Gofuku 3190, Toyama, 930-8555 Japan


Crystal structures of four simple azulene derivatives, 1,3-diheterolyl- and 1,3-diphenylazulenes, were determined by X-ray diffraction analysis. Three of them showed clear out-of-plane deformation of the azulene ring along its short molecular axis, and one showed a similar but very small deformation. Structural and conformational analyses on substituted azulenes were also performed by DFT molecular orbital calculations. Based on the results of the calculations it was indicated that azulenes could exhibit such deformation depending on their conformations except one case, supporting the results of X-ray analysis. A similar deformation was also found in the crystal structure of a previously reported 1,3-disubstituted azulene whose data were collected from an X-ray crystal structure database.