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Angular Dependence of the C-6 Chemical Shift and the Conformation of the Hydroxymethyl Group  in Carbohydrates*

K. Mazeau, F. R. Taravel, and I. Tvaroška

Centre de Recherches sur les Macromolécules Végétales (CERMAV), CNRS, BP 53, 38041 Grenoble cedex 9, France

 

Abstract: Semiempirical quantum-mechanical nuclear shielding calculations (FTP INDO method) have been performed on a series of 16 hexopyranoses for conformational studies of hydroxymethyl groups in carbohydrates. The calculated shielding for the C-6 and C-5 atoms shows an angular dependence of up to δ = 8 which is in agreement with that found experimentally. The dependence of the C-6 chemical shift on the dihedral angle omega is presented by a trigonometric function of the form δ(C) = A sin ω+B sin 2ω+C sin 3ω+D cos ω+E cos 2ω+F cos 3ω+G with different A-G constants for both series of hexopyranoses with different configuration at their C-4 atoms. This angular dependence may be applied for prediction of conformations about the C-5-C-6 bond in noncrystalline materials. It is also demonstrated that this dependence together with the angular dependence for C-5 atom, can be useful in estimating the conformational preferences of the hydroxymethyl group in carbohydrates in solution having the configurations at C-4 as in D-glucose and D-galactose.

Full paper in Portable Document Format: 502a77.pdf

 

Chemical Papers 50 (2) 77–83 (1996)

Monday, August 08, 2022

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