SUBSTITUENT EFFECTS ON C-13 CHEMICAL-SHIFTS OF AROMATIC CARBONS IN BETA-O-4 AND BETA-5 TYPE LIGNIN MODEL COMPOUNDS

Substituent effects on the chemical shifts of aromatic carbons in lignin model compounds have been elucidated from **1**3C NMR spectra of guaiacyl and syringyl type monomeric and beta -O-4 model compounds and guaiacyl type beta -5 model compounds. Evaluation of the observed values of substituent chemical shift (SCS) for the aromatic carbons leads to elucidation of a generalized SCS additivity rule, for estimation of the chemical shifts of aromatic carbons in ring A of beta -O-4 and beta -5 type substructures in model compounds and in ring B of beta -O-4 substructures in lignin preparations, with errors of less than 1 ppm.