C-13 NMR OF LIGNINS IN AQUEOUS ALKALI .2. IONIZATION EFFECTS ON THE SPECTRA OF TECHNICAL LIGNINS

Aqueous alkali is a convenient medium for obtaining C-13 NMR spectra o f lignins. The spectra of a series of model compounds were recorded in both aqueous alkali and a deuterated organic solvent that, with the d ata published previously, made up the basis for interpreting the spect ra of lignins in aqueous alkali and changes in chemical shifts upon io nization of functional groups in the polymer. The spectra of sample li gnins of distinctively different origin, i.e., ALCELL, oxygen-organoso lv, and kraft lignins were recorded and interpreted. It is shown that the spectra in aqueous alkali can be used in lignin characterization e xactly in the same manner as the spectra in an organic solvent. In add ition, ionization chemical shifts may be used as a structural probe. T his new technique brings valuable extention to C-13 NMR spectroscopy o f lignins.