Interpretation of the IR spectrum of methyl-β-D-glucopyranoside based on the theoretical calculation of frequencies and intensities of normal vibrations

Calculation of the structure and IR spectrum of methyl-β-D-glucopyranoside by density functional theory

“…These discrepancies were partly due to limitations of the harmonic approximation. These frequencies were closer to the experimental values in the previous work [17,18]. In our instance, the discrepancy was removed by scaling these frequencies.…”

“…A program set for calculating vibrational spectra of polyatomic molecules [19] that uses such an approach produced the results required to interpret IR spectra of the studied compounds and to predict and estimate quantitatively the influence of intermolecular interactions on the intensities of the IR absorption bands. A comparison of the calculated and experimental spectra of methyl-β-D-glucopyranoside enabled typical spectroscopic signatures of hydroxymethyl substitution of the hydroxyl on the first C atom of the pyranose ring and the principles involved in forming the structurally complicated band in the frequency range 1150-950 cm -1 to be found [17,18]. These explained the characteristic changes in the spectrum on going from β-D-glucose to methyl-β-D-glucopyranoside.…”

“…It was concluded [16] that non-empirical methods must be combined with semi-empirical methods in order to calculate IR spectra of monosaccharides. The IR spectrum of methyl-β-D-glucopyranoside that was recorded at room temperature was first interpreted [17,18] based on calculated frequencies of normal vibrations and absolute intensities of IR absorption bands that resulted from an original approach [19] combining classical and quantum-chemical semi-empirical methods. Results from the classical solution for normal vibrations using a valence-force field and from quantum-chemical calculations of the electronic structure of the molecule by the CNDO/2 semi-empirical method were used together to calculate absolute intensities.…”

“…Here results from modeling the structure and IR spectrum of an isolated methyl-β-D-glucopyranoside molecule in the harmonic approximation are compared with previous work [17,18].…”

“…Table 2 presents calculated frequencies of normal vibrations and peak intensities of IR absorption bands of the studied molecule and indicates assignments for observed bands in the spectrum of this compound according to vibration types and intensities. The data in Table 2 were also compared with analogous data from the literature [17,18].…”