Correlation of experimental and ab initio 13C-NMR chemical shifts for monomeric lignin model compounds

The C-13-NMR chemical shifts of monomeric model compounds representing the guaicyl, syringyl and p-hydroxyphenyl forms of lignin were calculated using ab initio GIAO methods and compared to experimental data fi om the literature. The least squares regression analyses of the results indicate R-square values in excess of 0.96 for the total dataset and upon sorting by compound. Sorting by carbon position gave less accurate results with the chemical shifts for a given location dependent on the parent compound and environment of the carbon atom in question. The ability of a substituent group to rotate, and therefore to alter the geometry of the system, was particularly marked. (C) 2000 Elsevier Science B.V. All rights reserved.