ABSORPTION SPECTRA AND PPP-MO CALCULATIONS OF THIOPYRAN AND RELATED COMPOUNDS |
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| Authors: | H Nakazumi T Ueyama T Kitaguchi T Kitao |
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| Institution: | Department of Applied Chemistry , College of Engineering, University of Osaka Prefecture , Sakai, Osaka, 591, Japan |
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| Abstract: | Abstract The absorption bands of the coumarin, the thiocoumarin and thiochromone have been examined by the PPP calculation with variable β approximation, changing with increasing ring size. The calculated longest-wavelengths (λ1) of these series were in good agreement with the experimental values measured in ethanol. A bathochromic displacement of λ1 produced by annelation of a benzene ring to a 2H-pyran-2-one, a coumarin and its thio analogues might be mainly due to a reduction of LUMO energy levels and/or increase of HOMO energy levels. The substituent effect on absorption spectra in the coumarin, the thiocoumarin and thiochromone series has also been examined, and discussed in terms of PPP calculations. |
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