Thesis - Open Access
Master of Science (MS)
Previous reflectance study in our laboratory has shown that stilbenes and azobenzenes adsorbed on alumina or silica undergo a more-or-less reversible loss of olefinic double bond character up on irradiation at appropriate wavelengths, and an intermediate was proposed. The purpose of this work was trying to characterize the intermediate using infrared technique. Stilbene exists in two isomeric forms. The molecular structure of trans-stilbene was found to be almost planar in the solid state with the phenyl rings only slightly twisted from the general plane of the molecule, 1 and a careful study by Suzuki indicates that it is safe to, assume the molecule to be planar in solution as well. The phenyl rings of cis-stilbene are twisted by about 30° to relieve the steric interaction effects in the ortho hydrogens. Both thermal and photoinduced isomerizations are known to occur. Thermal isomerization of cis - stilbene takes place both in solution and in the vapor phase. The energy of activation in solution is 46±2.0 kcal/mole4 and in the vapor phase 42.6±1.0 kcal/mole. The isomerization can occur either through the vibrationally excited ground state or the first excited triplet, where the olefinic bond has less double bond character. Isomerization in solution is catalyzed by radicals such as Br, Lewis acids like A1Cl3 and Broensted acids such as H 2SO4. All have the effect of removing the double bond character from the olefinic bond. In the above-mentioned studies of adsorbed stilbene, the resultant irradiation products were all identified following rapid removal from the surface of the solid matrix. A careful study by Hecht and Jensen13 indicates that trans-stilbene adsorbed on 150°C activated neutral alumina using vacuum line techniques showed a complete loss of the trans peak upon irradiation, followed by a slow return for 22.5 hours at 95°C. The intermediate for irradiated trans-stilbene adsorbed on alumina was also proposed.
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South Dakota State University
Shih, Chien, "Infrared Study of Adsorbed Trans-Stilbene and Azobenzene" (1981). Electronic Theses and Dissertations. 4054.