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

D.H.P. polymer model of Lignin was synthesized by enzymatic dehydrogenation of coniferyl alcohol enriched to 90% in 13 C‐γ, on the benzylic position. On the 1 H NMR spectrum recorded at 250 MHz, of the 13 C labelled D.H.P., the study of the J CH‐γ couplings, made possible a precise assignment of proton signals. The 13 C NMR spectra showed that the 13 C‐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 13 C‐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 J CH–γ couplings of these C‐γ carbon atoms were determined.