Collect. Czech. Chem. Commun.
1983, 48, 1829-1841
https://doi.org/10.1135/cccc19831829
Pertrimethylsilylation as a method for improvement of chemical shift additivity through conformational homogenization. 1H and 13C NMR spectra of pertrimethylsilylated derivatives of methyl β-D-xylopyranosides
Jan Schramla, Eva Petrákováb, Otomar Pihara, Ján Hirschb and Václav Chvalovskýa
a Institute of Chemical Process Fundamentals, Czechoslovak Academy of Sciences, 165 02 Prague 6-Suchdol
b Institute of Chemistry, Slovak Academy of Sciences, 842 38 Bratislava
Abstract
All possible mono-, di-, and tri- O-methyl, O-benzyl, O-benzoyl, and O-acetyl derivatives of methyl β-D-xylopyranoside were fully trimethylsilylated and their 1H and 13C NMR spectra measured in deuteriochloroform solutions. The spectra were analysed and the chemical shifts completely assigned on the basis of decoupling experiments. The proton-proton coupling constants vary only very little throughout the series. Conformer population analysis by the method of average coupling constants shows that trimethylsilylation increases the C1 conformer population and makes the series conformationally homogenous. Owing to this conformational homogeneity chemical shifts (both 1H and 13C) satisfy very well direct additivity rule. It is suggested that pertrimethylsilylation should be employed whenever deviations from chemical shift additivity are caused by conformational mobility of the investigated series of compounds and when bulky groups can stabilize one of the conformers.
