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Structure of the acetal segment in O-glycosides

I. Tvaroška and T. Kožár

Institute of Chemistry, Slovak Academy of Sciences, 809 33 Bratislava


Abstract: The dependence of bond angles and bond lengths of the acetal segment upon its conformation in O-glycosides was studied. For this purpose geometrical parameters of the acetal segment were calcd. from x-ray and neutron diffraction structural data for various glycosides and treated statistically. The calcd. mean values of geometrical parameters of the individual groups were analyzed from the point of view of their changes resulting from different dihedral angles Θ, Φ, and Ψ, as well as from the type of the glycosidic linkage. The obtained data were compared with those calcd. for the most stable conformation of 2-methoxytetrahydropyran by PCILO quantum chem. method. The most significant difference in the geometry of α- and β-glycosides is shortening of the C(1)-O(1) bond length by 2 pm in the latter (from 140.9 to 138.9 pm), and contraction of the O(5)-C(1)-O(1) and C(5)-O(5)-C(1) bond angle by 4 and 2°, resp., namely from 111.5 to 107.4° and from 114.1 to 111.8°. The geometrical changes obsd. for the acetal segment as a result of the changed conformation are interpreted in terms of the mutual equil. of steric interactions and delocalization of lone electron pairs at the O atoms.

Full paper in Portable Document Format: 354a425.pdf


Chemical Papers 35 (4) 425–440 (1981)

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