Analysis of hydroxyl groups in lignins by H-1 NMR spectrometry

Milled wood lignins (MWL) were analysed by H-1 NMR spectrometry at 400 MHz (DMSO-d(6) solution). It was found that the signal from phenolic groups in lignin models representative of "condensed" lignin units in general are loc ated at comparatively high field (in the range delta 8.0-8.5). An exception is 2-methoxy-4-(1-methoxyethyl)-6-[2-methoxy-4-(1-methoxyethyl)phenoxy]phe nol (the ArOH signal is located at delta 8.65). p-Coumarate groups in maize lignin and p-hydroxybenzoate groups in poplar lignin were analysed. Differ ence spectra obtained by subtraction of the spectrum recorded after additio n of CF3COOD from the original lignin spectrum revealed the occurrence and approximate amounts of secondary and primary alcohol groups in MWL. MWL fro m both spruce wood and birch wood exhibit a peak at delta approximate to2.8 that is assigned to HE in erythro forms of beta -1 structures. A peak at d elta 2.88 in birch lignin spectra is attributed to H beta in three forms of such structures.