Fig. 8
Two-dimensional (2D) NMR spectra (HSQC experiments) at the gel state of: the lignin structures identified are shown: (A) β-O-4′ substructure; (B) resinol substructure; (C) phenylcoumaran substructure;  (D) spirodienone substructure; (G) guaiacyl unit; (S) syringyl unit; (S′) Cα-oxidized S unit; (E) α, β-diaryl ether substructures; (H) para-hydroxy-phenyl unit (R, lignin or OH; R′, H or lignin)