Structural features of lignins and humic substances as revealed by spin-echo and broadband decoupled C-13 NMR spectroscopy

Abstract The C-13 NMR spectra of native aspen and native spruce lignin were used to interpret the spectra of Kraft lignins and selected humic substances. The nature and extent of side chain degradation, as well as changes in phenolic content, were clearly revealed in the Kraft lignin spectra. Evidence for residual lignin fragments was obvious in the spectra of the peat humic substances. Stream fulvic acid spectra revealed clear evidence of aromatic CH character. Soil fulvic acid, on the other hand, appeared to have a more highly condensed aromatic ring character than stream fulvic acid. The simplest spectrum was shown by the ground water fulvic acid.