Table 3 Assignments of 13C-1H correlation signals in the HSQC spectrum of lignin samples [26, 27]
Signals | δC/δH | Assignments |
|---|---|---|
MeO | 55.4/3.72 | C-H in methoxyls |
A γ | 59.5–59.7/3.40–3.63 | Cγ-Hγ in β-O-4′ substructures (A) |
A α | 71.6/4.88 | Cα-Hα in β-O-4′ substructures linked to a S unit (A) |
Aβ(G), Aβ(S) | 82.8–85.7/4.13–4.46 | Cβ-Hβ in β-O-4′ substructures linked to a G unit (A) Cβ-Hβ in β-O-4′ substructures linked to a S unit (A) |
S2, 6 | 103.8/6.69 | C2,6-H2,6 in etherified syringyl units (S) |
S′2, 6 | 106.4/7.31 | C2, 6-H2, 6 in oxidized (Cα= O) phenolic syringyl units (S′) |
G5 | 115.1/6.72 | C5-H5 in guaiacyl units (G) |
G2 | 111.0/7.02 | C2-H2 in guaiacyl units (G) |
G6 | 119.0/6.77 | C6-H6 in guaiacyl units (G) |
FA2 | 110.8/7.35 | C2-H2 in FA |
FA6 | 123.1/7.16 | C6-H6 in FA |
FA7 | 144.4/7.42 | C7-H7 in FA |
H2, 6 pCA | 127.5/7.23 129.8/7.52 143.9/7.51 | C2, 6-H2, 6 in H units (H) C2, 6-H2, 6, p-coumaroylated substructures (pCA) Cα-Hα, p-coumaroylated substructures (pCA) |
115.0/6.24 | Cβ-Hβ, p-coumaroylated substructures (pCA) |