Ir spectra of triphenyl phosphite and their interpretation by molecular modeling

Background and Objectives: IR spectra of triphenyl phosphite (TPhPh) were measured in liquid (at 320 K), glassy and glacial phases and in hexagonal (metastable) and monoclinic (stable) crystal phases at 12 K. The observed differences in the spectra is a consequence of the implementation of the conformers of different types in the sample. To substantiate this hypothesis, structurally dynamic models of the three most probable conformers (I –III) were built. The conformers are different in angles of rotation of the phenyl rings around the C-O bonds. Materials and Methods: Molecular modeling performed by the density functional theory B3LYP / 6-31G (d) using GAUSSIAN 03 software package. Results: The energies, geometric parameters, force constants, dipole moments, frequencies and forms of normal vibrations and their intensities in the IR spectra for conformers I–III were calculated. The calculated geometric parameters lie within the limits allowed for structural chemistry. The measured and calculated IR spectra were analyzed and interpreted. The differences of the IR spectra are shown in the areas of deformation vibrations of the O-P-O (700–750 cm $^{-1}$), the stretching vibrations of P-O (840–890 cm $^{-1}$) and C-O (1180–1220 cm $^{-1}$). Conclusion: It was found that the experimental spectra of the glass phase, liquid phase and the state «glacial» are a superposition of the IR spectra conformers I–III. The conformer close to conformer I is created at hexagonal and monoclinic phases. A weak hydrogen bond is possible to be formed in the sample.