The Spatial Configurations and the Ultraviolet Absorption Spectra of the Stilbene Derivatives

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Abstract
(1) With certain simple assumptions, calculations based on the molecular orbital method have been performed to assess the quantitative relations between the degree of the deviation from the coplanarity of the molecular configuration and the ultraviolet absorption spectrum as well as the resonance energy for the stilbene derivatives. (2) New measurements of the spectra of the several stilbene derivatives have been carried out. (3) By these calculations and the measurements of the spectra, it has been clarified that the absorption maximum is shifted progressively toward shorter wave lengths with the increasing angle of twist of the phenyl groups out of the plane of the ethylenic linkage. (4) Further, from the results of these calculations and the observed position of the absorption maximum, it is possible to deduce the adequate values of the angle of twist and the resonance energy for any stilbene derivative. (5) It has been shown that the absorption spectra for the trans isomers and those for the cis isomers of the stilbene derivatives from two groups quite distinct from each other in hat the former shows a larger moleculart extinction coefficient than the latter. On the basis of this fact, the assignements of the geometrical configurations have been determined for some stilbene derivatives. (6) The experiments on the geometrical isomerization of α, α’-dimethylstilbene by heat have been carried out and the results have been carried out and the results have been interpreted, based on a consideration of the spatial configurations of the two isomers.