13C nuclear magnetic resonance spectral study on the distribution of substituents in relation to the preparation method of partially acetylated dextrans

Abstract

Abstract 13C nuclear magnetic resonance (n.m.r.) spectra of partially modified dextrans with acetyl groups prepared by reaction with acetyl chloride or acetic anhydride in the homogeneous phase were analysed at 75.4 MHz. It was found that the distribution of substituents in the anhydroglucose units of these partially acetylated dextrans can be estimated from their ring carbon spectra. The results showed that for acetylated dextrans prepared by reaction with acetyl chloride, the reactivity of individual secondary hydroxyl groups decreases in the order C-2 > C-4 > C-3. For those modified dextrans prepared with acetic anhydride, the ease of acetylation was C -2⋍ C -3 > C -4 . The results were explained by considering the formation of intramolecular hydrogen bonds as well as by steric considerations.