A polymer model of lignin (D.H.P.) 13C selectively labelled at the benzylic positions: Synthesis and NMR study

Abstract

AbstractD.H.P. polymer model of Lignin was synthesized by enzymatic dehydrogenation of coniferyl alcohol enriched to 90% in 13C‐γ, on the benzylic position. On the 1H NMR spectrum recorded at 250 MHz, of the 13C labelled D.H.P., the study of the JCH‐γ couplings, made possible a precise assignment of proton signals. The 13C NMR spectra showed that the 13C‐γ carbon atom previously labelled in coniferyl alcohol was found in several sites in the polymer. Special NMR techniques like gate decoupling and selective proton irradiation were used together with the study of the chemical shifts, to make an assignment for the different 13C‐γ signals. C‐γ in carbonyl compounds like vanillin and vanillic acid, C‐γ vinylic atom like in coniferyl alcohol and cinnamaldehyde. C‐γ atom like in β5, ββ, βO4 dilignol units, and C‐γ atom involved in C‐γ benzyl ether bond in βO4 dimer were identified; the corresponding JCH–γ couplings of these C‐γ carbon atoms were determined.