Table 3.
Assignments of main lignin 13C-1H correlation signals for the lignin substructures shown in Figure 7 and observed in the lignin 2D-heteronuclear single quantum coherence nuclear magnetic resonance spectra (Figure 5 and Figure 6).
| Label | δC/δH | Assignement |
|---|---|---|
| OCH3 | 55.6/3.73 | C−H in methoxyls |
| Aγ | 59.4/3.40–3.72 | Cγ−Hγ in β-O-4′ substructures (A) |
| A′γ | 63.8/3.83–4.30 | Cγ−Hγ in γ acetylated β-O-4′ substructures (A′) |
| Bγ | 62.5/3.66 | Cγ−Hγ in β-5′ phenylcoumaran substructures (B) |
| Aα | 71.8/4.86 | Cα−Hα in β-O-4′substructures (A) |
| Iγ | 61.4/4.10 | Cγ−Hγ in p-hydroxycinnamyl alcohol end groups (I) |
| Cβ | 53.5/3.05 | Cβ−Hβ in β-β′resinol substructures (C) |
| X5 | 62.6/3.40–3.72 | C5-H5 in β-D xylopyranoside |
| HKα | 47.4/3.62 | α-protons in Hibbert ketone (HK) structure |
| HKγ | 66.2/ 4.2 | γ-protons in Hibbert ketone (HK) structure |
| G5 | 114.9/6.77 | C5−H5 in guaiacyl units (G) |
| H3,5 | 114.5/6.62 | C3,5−H3,5 in p-hydroxyphenyl units (H) |
| H2,6 | 128.3/7.22 | C2,6−H2,6 in p-hydroxyphenyl units (H) |
| PCA3.5 | 115.8/6.83 | C3,5–H3,5 in p-coumarate (PCA) |
| Phe | 126.9/7.16 | Phenylalanine (residual proteins) |
| Tyr | 130.5/7.0 | Tyrosine (residual proteins) |