H-1-NMR OF ACETYLATED BETA-ETHER BETA-ETHER LIGNIN MODEL TRIMERS

Detailed examination of the H-1 NMR spectra of acetylated beta-ether/b eta-ether lignin model trimers, particularly those synthesized with pa rtially defined stereochemistry, revealed that all of the eight chemic ally distinct isomers (sixteen optical isomers from four optical cente rs) are detectable. These compounds provide excellent models for both internal (etherified) and terminal (free-phenolic) units in lignin and clearly delineate the chemical shifts for each isomer. High-field two -dimensional TOCSY or relayed coherence transfer NMR experiments allow correlation of all the side-chain protons in each isomer, while J-res olved experiments clearly show the presence of all expected isomers. T he degree of complexity already encountered with these simple compound s points to the overwhelming improbability of finding even small cryst alline regions in lignin.