APPLICATION OF 3-DIMENSIONAL HMQC-HOHAHA NMR-SPECTROSCOPY TO WOOD LIGNIN, A NATURAL POLYMER

The three-dimensional HMQC-HOHAHA experiment was successfully applied to an acetylated C-13-enriched poplar wood lignin preparation. The res olution of this technique proved to be sufficient to give unambiguous assignments for most of the side-chain structures, which overlap heavi ly in one- and two-dimensional NMR spectra. By this technique it was p ossible to show, for the first time, that alpha,beta-diaryl ether stru ctures exist in lignin, although in low abundance. These structures ha ve been considered to be of importance in lignin structure, since they may act as reactive crosslinking groups providing the lignin polymer with a branched network structure.