A theoretical study of the structure and vibrational spectrum of methyl-β-D-glucopyranoside is performed with allowance for the hydrogen bond effect on them. At the density functional theory level with the use of the B3LYP functional in the 6-31G(d) basis set the structural dynamic models of a free molecule of methyl-β-D-glucopyranoside and its simplest complexes with hydrogen bonding in the form of dimers with different structures are constructed. Energies are minimized; structures, electro optical parameters, force constants, and normal vibrational frequencies in the harmonic approximation and their intensities in IR spectra are calculated; the hydrogen bond energy is estimated. Based on the calculation, the conclusions are drawn about the structure of the methyl-β-D-glucopyranoside sample, the formation and interpretation of its IR spectrum, and the possibilities of the used density functional theory method.

539.194 Structural-dynamic models of methyl-β-D-glucopyranoside have been constructed by a density functional method using a B3LYP functional in bases 6-31G(d) and 6-31+G(d,p). Energies have been minimized. Structures, dipole moments, polarizabilities, frequencies of normal modes in the harmonic approximation, and the intensity distribution in the molecular IR spectrum have been calculated. The calculation results have been compared with both the experimental spectra of methyl-β-D-glucopyranoside in the region 400-3700 cm -1 and data obtained within the framework of an approach that uses the classical valence-force method to calculate normal mode frequencies and the quantum-chemical CNDO/2 technique to calculate the electronic structure.Introduction. The construction of structural-dynamic models of molecules and molecular systems based on quantum-mechanical methods has become an essential part of research on the structure, optical spectra, and properties of compounds. The accuracy of quantum-mechanical calculations has risen significantly during the last three decades. This made it possible to use them in molecular spectroscopy. The satisfactory agreement of theoretical and experimental spectra provides indirect confirmation that the selected quantum-mechanical methods and approximations are correct and precise. The discrepancy between calculated harmonically and measured fundamental vibration frequencies is less than 4-5%. This enables the results of such calculations to be used to interpret measured vibrational spectra. The absolute error within the limits of this uncertainty turns out to be different for frequencies of normal vibrations. It is 150-200 cm -1 in the high-frequency range (2850-3750 cm

539.194 The IR spectrum and structure of methyl-β-D-glucopyranoside have been studied theoretically taking into account the influence on them of the hydrogen bond formed in the sample. Density-functional theory with the B3LYP functional in basis 6-31G(d) was used to minimize the energies and calculate the structures, electrooptical parameters, force constants, frequencies of normal harmonic vibrations, and intensities in IR spectra of the simplest H-bonded dimeric complexes of methyl-β-D-glucopyranoside. The calculated spectra of Hbonded complexes were compared with those of the free molecule and the experimental spectrum in the range 400-3700 cm -1 . Conclusions about the structure of methyl-β-D-glucopyranoside were made. The interpretation of its IR spectrum was refined.