The geometry of the 4′-cyano-(4′-CNPTB) and the 4′-methoxy-(4′-MePTB) phenylthiolbenzoates were obtained by ab initio calculations employing 6–31G basis set at Hartee-Fock level of theory. The results predict an extended form of the molecules and torsional angle between the phenyl rings at 90.85(6)0 and 90.87(3)0, respectively. On the basis of vibrational analysis the frequency assignment was carried out. The calculated frequencies were compared with the experimental IR spectral data in carbon tetrachloride, carbon disulfide solutions and in solid state.
The IR-spectra of 4-aminopyridine (4-AP) in solution and in the solid state have been analyzed, using the reducing-difference procedure. Defining a more precise band assignment of a part of the characteristic frequencies of 4-AP, the data obtained proved in particular a Fermi-resonance splitting of the symmetric NH2-stretch.
The UV-photoinduced prototropic isomerization of 1,3-diphenyl pyrazol-5-one (DPhP) embedded in polyvinyl chloride (PVC) film is studied by means of difference in IR spectral analysis. The initially existing CH-form in non-irradiated compound is transformed to NH-form, and a hydrochloride salt is stabilized because of the photodegradation of the PVC. An additional comparative IR spectral study of DPhP in different solutions as well as of its hydrochloride salts in solid state is also carried out.
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