1H NMR study of methyl O-acetyl-α and -β-D-xylopyranosides : conformational studies and non additivity of 1H-shift increments

1H NMR spectra of the complete series of fully and partially acetylated methyl α-and β-D-xylopyranosides have been studied. The α-anomers occur exclusively in 4C1 chairs but the 1C4 chair becomes increasingly populated in the β-forms especially when the OH-3 is not acetylated. Increments used for the prediction of the chemical shifts of ring protons are discussed and compared with the literature data. The predictability for changes in shifts upon acetylation is poor.1H NMR spectra of the complete series of fully and partially acetylated methyl α-and β-D-xylopyranosides have been studied. The α-anomers occur exclusively in 4C1 chairs but the 1C4 chair becomes increasingly populated in the β-forms especially when the OH-3 is not acetylated. Increments used for the prediction of the chemical shifts of ring protons are discussed and compared with the literature data. The predictability for changes in shifts upon acetylation is poor.A