Determination of the Distribution of Substituent Groups in Sodium Cellulose Sulfate: Assignment of 1H and 13C NMR Peaks by Two-Dimensional COSY and CH-COSY Methods

Abstract

An attempt was made to give full assignment to the 1H and 13C NMR spectra of sodium cellulose sulfate (NaCS) dissolved in D2O and to determine the molar fractions of all possible 8 kinds of anhydroglucopyranose (AHG) units constituting NaCS molecule. For this purpose five NaCS samples with the total degree of substitution «F» ranging from 0.61 to 2.42 were synthesized by three different methods. Using a NaCS sample («F»=2.42) 1H and 13C peaks for 2,3,6-trisubstituted AHG were reasonably assigned by two-dimensional (2D) homonuclear 1H correlation spectroscopy (COSY) and heteronuclear 1H-13C correlation spectroscopy (CH-COSY) techniques. In the same manner, 1H and 13C NMR peaks originating from unsubstituted AHG were assigned by analysis on NaCS with «F»=0.61. Chemical shifts (δ) of protons and carbons in monosubstituted and disubstituted AHG units were calculated using shift factors empirically estimated from the observed δ values of trisubstituted and unsubstituted AHG units. The assignments on 1H NMR peaks for NaCS previously made by Kamide and Okajima [Polym. J., 13, 163 (1981)] on the basis of the peak assignment of cellulose acetate were found to be partly incorrect. The average degree of substitution for each three hydroxyl groups attached to C2, C3, and C6 carbon positions «fk» (k=2, 3, and 6) was estimated based on the assignment made here and a relation «f6»>«f2»>«f3» was obtained for the NaCS samples synthesized here.