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For the first time, we have assigned the observed absorption bands and interpreted the IR spectrum of methyl-β-D-glucopyranoside in detail in the 1500-800 cm -1 region, based on a full calculation of the frequencies and absolute intensities of the normal vibrations of the molecule and their comparison with the experimental data. We have identified two groups of spectral signs indicating an oxymethyl substituent has replaced the hydroxyl group on the C (1) atom in the glucopyranoside: absorption bands of medium intensity due to the characteristic vibrations of the substituent, and intense bands due to an unusual "interaction" between many structural moieties.Introduction. Vibrational spectroscopy is undoubtedly one of the most widespread methods for structural analysis of compounds, and it has found broad application in solving a number of problems of practical importance. We should note that the connections between the vibrational spectra and the structure of molecules are complex and distinctive. Consequently, as the molecules become more complicated, interpretation of the spectra requires drawing on as extensive a set of experimental data as possible (the results of analysis of other parameters, besides the frequencies, of the IR absorption bands and the lines in the Raman spectra; in a number of cases, study of the spectra of deuterated derivatives, etc.) and theoretical analysis of the molecular vibrations.Theoretical study of the spectra of specific classes of complicated compounds requires special procedures and approaches, and ignoring this fact may lead to significant reduction in the obtainable data, and often to insufficiently substantiated and erroneous conclusions. Such compounds include carbohydrates in particular.Properties of monosaccharides that are of practical value are mainly determined by the steric arrangement (conformation, configuration) of the individual groups of atoms determining the system of intramolecular and intermolecular interactions. But extracting information about the fine details of the structure of carbohydrates from observed vibrational spectra is an extremely difficult task, due to the complexity of the structure of these compounds, the strong dependence of their spectra on steric factors, and the diversity of the conformational forms of the molecules. A necessary condition for correct interpretation of vibrational spectra of monosaccharides and their derivatives is a full calculation of the frequencies and intensities of the molecular vibrations for these compounds. In this case, systematic study of whole classes of compounds with gradually more complicated molecular structures is especially important.Extensive experimental data on the vibrational spectra of carbohydrates has been accumulated and systematized at the Institute of Physics (National Academy of Sciences of Belarus) under the direction of R. G. Zhbankov [1][2][3][4][5]. A special procedure has been developed and an original software package has been created to calculate the frequencies, modes, potential energy d...

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