A COMPARISON OF SOLUTION AND SOLID-STATE C-13 NMR-SPECTRA OF LIGNINS AND LIGNIN MODEL COMPOUNDS

The solution and magic angle spinning (MAS) C-13 NMR spectra of a comprehensive series of monomer and dimer lignin model compounds are reported. Most chemical shifts from solid state spectra are similar to those from the solution state, however a significant number of resonances do have substantial (4 to 9 ppm) solution-solid state chemical shift differences. The large differences are most likely the result of conformational changes on passing from the solid to the solution state. From the solid state spectra of the model compounds a table is presented of selected chemical shift ranges for selected carbon environments. It was found that under a standard set of experimental conditions the non-protonated carbon resonances from model sompound spectra gave reliable integrations. The same technique was applied to the spectra of 5 lignins from different sources and the degree of condensation and the syringyl/guaiacyl ratio of the lignins is discussed.