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Theoretical-studies on the conformation of saccharides .11. Stereochemistry of methyl α-D-glucopyranosides and methyl β-D-glucopyranosides in solution

I. Tvaroška and T. Kožár

Institute of Chemistry, Centre for Chemical Research, Slovak Academy of Sciences, CS-84238 Bratislava

 

Abstract: Stereochemistry of methyl a-D-glucopyranoside and methyl β-D-glucopyranoside in ten solvents has been studied theoretically. The energy of 14 basic forms of pyranose ring of methyl  α- and methyl β-D-glucopyra- nosides was calculated by the PCILO quantum-chemical method. The calculated geometries of chair forms of both molecules were found to be in reasonable agreement with the available data obtained by X-ray diffraction of pyranosides. The stability of two axial and three equatorial chair confor­med in solution was compared by using a method where the total Gibbs energy included the Gibbs energy of the isolated molecule and solvation Gibbs energy. Solvation Gibbs energy encompasses electrostatic, dispersion, and cavity terms. The calculated abundance of methyl α-D-glucopyranoside 63 % in methanol solution is in good agreement with the value 67 % found experimentally. The calculated values of exo-anomeric effect decrease with the increasing polarity of the solvent and are in the range of 3.7—4.0kJmol-1 for methyl α-D-glucopyranoside and 3.8—4.6 kJ mol-1 for methyl ß-D-glucopyranoside.

Full paper in Portable Document Format: 414a501.pdf

 

Chemical Papers 41 (4) 501–510 (1987)

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