Table 1.
Structural assignments in 13C-NMR spectra of LS, 1-CPRLS, and 5-CPELS in DMSO-d6 solutions based on the spectra in Figure 3.
| Selected Groups (ppm) | δExp. (ppm) | Peak Assignment According to Literature Data | δ (ppm) | ||
|---|---|---|---|---|---|
| LS | 1−CPRLS | 5−CPELS | |||
| Carbonyl C (C = O) (200.0–160.0) [85] |
- | 178−174 | 179−177 | Carboxylic acid units | 173.0 [86], (172.8–171.2, 170.7–168.8) [76], 172.8 [81] |
| Aromatic C–O (ArC3, C4) (160.3–144.0) [75] * (160.0–140.0) [76] (154.6–140.7) [93] |
148–136 | 160–141 | 156–140 | ArC4 in H-type units | 157.8 [75] *, 156.4 [67,78] |
| ArC3/C3′ in etherified 5-5 units | 152.1 [67] | ||||
| ArC4 in etherified G-type units with αC = O | 151.3 [75] * | ||||
| ArC3 in etherified G-type β-O-4 units | (151.5–151.1) [75] *, 149.1 [67] | ||||
| ArC3 in etherified G-type units | 149.7 [89], 149.4 [67,77], 149.0 [75] * | ||||
| ArC3/C3′ in pinoresinol structure | 148.6 [74] | ||||
| ArC4 in etherified G-type units | 148.2 [75] *, 146.8 [67,77,89] | ||||
| ArC3 in non-etherified G-type β-O-4 units | (148.7–148.1) [75] *, 146.6 [67] | ||||
| ArC4 in non-etherified G-type β-O-4 units | (147.1–146.6) [75] *, 145.8 [67,77,89] | ||||
| ArC4/C4′ in pinoresinol structure | 146.7 [74] | ||||
| ArC4/C4′ in etherified 5-5 units | 145.0 [74] | ||||
| ArC4/C4′ in non-etherified 5-5 units | 144.0 [75] *,143.3 [67,89] | ||||
| ArC4 in ring β of β-5 units | 143.3 [67,89] | ||||
| Aromatic C–C (ArC2,C5 condensed) (140.7–123.4) [93] (140.3–122.9) [93] * (140.0–123.0) [76] |
136–114 | 141–118 | 140–118 | ArC1 in etherified G-type units | 137.5 [75] *, 134.6 [67,77] |
| ArC1/C1′ in pinoresinol structure | 132.9 [74] | ||||
| ArC5/C5′ in etherified 5-5 units | 132.4 [67,77,89] | ||||
| ArC1 in non-etherified 5-5 units | 131.2 [75] *, 131.1 [67,89] | ||||
| ArC2/C6′ in H-type units | 128.6 [92], 128.1 [67], 128.0 [86] | ||||
| ArC5/C5′ in non-etherified 5-5 units | 126.8 [75] *, 125.9 [67,77,89] | ||||
| Aromatic C–H (ArC2,C5,C6–H) (131.5–108.5) [50] * (123.4–105.3) [67] (123.0–103.0) [51] |
113–106 | 118–107 | 118–100 | ArC6 in G-type units | (125.2–120.0) [75] *, 124.0 [75], (123.0–117.0) [76], (119.9, 119.4, 118.4) [67,89], 118.4 [77] |
| ArC5 in G-type units | (118.1–111.4) [75] *, (117.0–114.0) [76], (115.1, 114.7) [67,77,89] | ||||
| ArC5/C5′ in pinoresinol structure | 115.7 [74] | ||||
| ArC3,C5 in H-type units | 115.0 [75] | ||||
| ArC2 in G-type units | (115.2–111.3) [75] *, (114.0–108.0) [76], (111.1–110.4) [67,89] | ||||
| ArC2/C2′ in pinoresinol structure | 110.3 [74] | ||||
| Cα,Cβ, Cγ
(90.0–58.6) [93] (89.8–58.6) [93] (81.9–56.3) [75] * |
80–58 | 86–59 | 89–60 | Cβ in β-O-4, Cα in β-5 and β-β units | (90.0–82.5) [88], (90.0–78.0) [76] |
| Cα in pinoresinol structure | 87.0 [74] | ||||
| Cα in β-5 and G-type β-5 units | 86.7 [92], 86.6 [67,89], (68.2–68.7) [75] * | ||||
| Cβ in G-type β-O-4 units | (84.6–83.8) [67],84.2 [92], (81.9–77.7) [75] * | ||||
| Cα, Cγ in β-β units | (84.3, 71.1) [92] | ||||
| Cα in β-O-4 and G-type β-O-4 units | (78.0–67.0) [76], 72.8 [92], (71.8, 71.2) [67,89], 71.2 [77], (68.0, 66.7) [75] * | ||||
| Cγ in β-β units | 72.4 [89] | ||||
| Cγ in pinoresinol structure | 72.3 [74] | ||||
| Cγ in β-O-4 and G-type β-O-4 units with αC = O | 63.2 [67,89], 53.7 [75] * | ||||
| Cγ in G-type β-5 and β-1 units | 62.8 [67,77,89] | ||||
| Cγ in β-O-4 and G-type β-O-4 units (without αC = O) | (62.8, 62.7) [75] *, (61.3–58.0) [76], 60.2 [67,77,89], (59.0–61.0) [88] | ||||
| Methoxyl, Cβ in β-β and β-5 units (52.0–58.0) [76] |
58–52 | 59–54 | 59–53 | Methoxyl (-OCH3) | (58.0–54.0) [76], 56.5 [92], 56.2 [74], 56.0 [62,86,87], 55.6 [67,89] |
| Methoxyl and Cβ in β-5 units | (58.1–52.5) [93], (56.5–52.0) [75] * | ||||
| Cβ in pinoresinol structure | 54.8 [74] | ||||
| Cβ in β-β and β-5 units | (54.0–53.0) [88], (54.0–52.0) [76] | ||||
| Cβ in β-β units | 53.8 [77], 53.9 [67,89] | ||||
| Cβ in β-5 units | 53.4 [67,77,89] | ||||
| Alkyl C (10.0–45.0) [90] (0.0–45.0) [86] |
- | 27–8 | 38–22 | Terminal methyl (-CH3) and methylene (-CH2-) in saturated aliphatic chain | 45–10 [90], 41.2–12.1 [75] *, 26.7 [89] |
| Methylene groups in aliphatic rings and side chains | 45–25 [86], 29.2 [89], 27 [76] | ||||
| Terminal methyl groups | 25–0 [86], 12–15 [76], 14.0 [89] | ||||
* Lignosulfonate assignments in MeOH-d4. The 13C solvent shifts Δδ1 = δ(DMSO)−δ(MeOH-d4) varies from −3.25 to +4.06 ppm [94]. The change in chemical shift of the sulfonated compounds compared to the corresponding compound with a hydroxyl group was reported in MeOH-d4. Significant chemical shift differences, Δδ2, are observed for the 1, 2, 6, α and β-positions, of approximately +7, −3.5, −4, +(6–8) and +5 ppm for 13C NMR. Smaller changes are observable for γ-position, whereas the other positions only show minor changes [75]. Carbon elements in dimethyl sulfoxide appear at 39.5 [88] (or 39.53 ± 05) ppm [88].