Table 3.
Signal assignments of the 13C−1H correlation peaks in the 2D HSQC NMR spectra of the isolated lignin fractions, according to Christensen [17], del Rio et al. [33], Kim and Ralph [34], Lourenço et al. [35], Noguchi et al. [36] and Ralph et al. [39]. The labels correspond to the respective lignin substructures shown in Figure 4.
| δC/δH (ppm) | Assignment (label) |
|---|---|
| 53.4/3.44 | Cβ-Hβ in phenylcoumaran β-5′ substructures (Bβ) |
| 53.9/3.05 | Cβ-Hβ in resinol substructures β-β′ (Cβ) |
| 60.0/2.96‒3.82 | Cγ-Hγ in γ-hydroxylated β-O-4′ substructures (Aγ) |
| 62.8/3.19 | C5-H5 in β-d-xylopyranoside (X5) |
| 63.2/3.69 | Cγ-Hγ in phenylcoumaran β-5′ substructures (Bγ) |
| 64.0/4.29 | Cγ-Hγ in γ-acylated β-O-4′ substructures (Aγ′) |
| 71.2/3.78 + 4.16 | Cγ-Hγ in resinol substructures β-β′ (Cγ) |
| 72.0/4.79 | Cα-Hα in β-O-4′ substructures (Aα) |
| 72.9/4.48 | C2-H2 in 2-O-acetyl-β-d-xylopyranoside (X′2) |
| 74.7/3.22 | C3-H3 in β-d-xylopyranoside (X3) |
| 75.8/4.87 | C3-H3 in 3-O-acetyl-β-d-xylopyranoside (X′3) |
| 77.2/3.50 | C4-H4 in β-d-xylopyranoside (X4) |
| 82.1/4.73 | Cα-Hα in benzyl ether substructures (BEα) |
| 82.0/4.55 | Cβ-Hβ in β-O-4′ substructures (Aβ(H)) linked to a H unit |
| 83.7/4.84 | Cα-Hα in dibenzodioxocin substructures (Dα) |
| 83.9/5.19 | Cβ-Hβ in α-oxidized (Cα=O) β-O-4′ substructures (Aoxβ) |
| 84.3/4.33 | Cβ-Hβ in β-O-4′ substructures (Aβ(G)) linked to a G unit |
| 85.2/4.62 | Cα-Hα in resinol β-β′ substructures (Cα) |
| 85.9/3.86 | Cβ-Hβ in dibenzodioxocin substructures (Dβ) |
| 86.8/4.06 | Cβ-Hβ in β-O-4′ substructures (Aβ(S)) linked to a S unit |
| 87.7/5.50 | Cα-Hα in phenylcoumaran β-5′ substructures (Bα) |
| 97.9/6.91 | C7-H7 in alfafuran (AF7) |
| 101.6/6.22 | C4′-H4′ in alfafuran (AF4′) |
| 102.8/6.32 | C5-H5 in chlorophorin (CP5) |
| 104.1/6.64 | C2,6-H2,6 in syringyl units (S2,6) |
| 104.2/6.86 | C3-H3 in alfafuran (AF3) |
| 106.9/6.16 | C2′,6′-H2′,6′ in chlorophorin (CP2′,6′) |
| 107.0/7.05 | C2,6-H2,6 in sinapaldehyde units (SA2,6) |
| 107.0/7.25 | C2,6-H2,6 in α-oxidized (Cα=O) syringyl units (S′2,6) |
| 107.1/6.46 | C2′,6′-H2′,6′ in alfafuran (AF2′,6′) |
| 107.4/6.81 | C4-H4 in alfafuran (AF4) |
| 107.5/6.46 | C3-H3 in chlorophorin (CP3) |
| 111.3/7.30 | C2-H2 in ferulic acid (FA2) |
| 111.3/7.01 | C2-H2 in guaiacyl units (G2) |
| 112.5/6.67 | C3,5-H3,5 in p-hydroxyphenyl units (H3,5) |
| 112.6/7.49 | C2-H2 in oxidized guaiacyl units (G′2) |
| 113.2/7.30 | C2-H2 in coniferaldehyde (CA2) |
| 115.9/6.96 + 6.63 | C5-H5 and C6-H6 in guaiacyl units (G5, G6) |
| 119.1/6.84 | C6-H6 in guaiacyl units (G6) |
| 119.5/6.84 | C6-H6 in coniferaldehyde (CA6) |
| 123.0/7.12 | C6-H6 in ferulic acid (FA6) |
| 125.0/6.74 | C7-H7 in chlorophorin (CP7) |
| 123.7/7.58 | C6-H6 in oxidized guaiacyl units (G′6) |
| 125.0/6.73 | Cβ-Hβ in cinnamyl aldehyde end groups (CAβ) |
| 128.9/7.14 | C2,6-H2,6 in p-hydroxyphenyl units (H2,6) |
| 129.6/7.91 | C2,6-H2,6 in p-coumaric acid (pCA2,6) |
| 145.2/7.46 | Cα-Hα in p-coumaric and ferulic acid (pCAα, FAα) |
| 154.0/7.60 | Cα-Hα in cinnamyl aldehyde end groups (CAα, SAα) |