Carbon-13 NMR Spectra of Lignins, 10.1 Comparison of Structural Units in Spruce and Beech Lignin

Abstract 90.7 MHz Carbon-13 NMR spectra of spruce and beech milled wood lignins (MWLs) and comparison with the spectra of their acetates as well as acetylated dehydrogenation polymer (DHP) from coniferyl alcohol reveals detailed information on the constitution of the two lignins. The signals indicative of β-0-4 units are split, due to the occurrence of erythro and threo isomers. In beech lignin erythro β-0-syringyl ethers by far prevail in the β-0-4-linkages. The spectra also provide unequivocal evidence for the occurrence of β-5 and β-β linkages in both spruce and beech lignins, while some anomalies remain in the case of β-1 and α,β-bis-0-4 units. Two-dimensional 13C-J(1H)-NMR spectra of acetylated DHP corroborate the assignment of signals in the spectra of acetylated MWLs.