Table 3. Relative Abundance of Lignin Interunit Linkages and Aromatic Units of 12C/13C Lignin Isolates by Semiquantitative HSQC NMR Analysis.
| 12C-LIGpure | 13C-LIGpure | |
|---|---|---|
| Lignin interunit linkages (%)a | ||
| β-O-4′ aryl ethers (A/A′) | 80 | 81 |
| α-oxidized β-O-4′ aryl ethers (Aox) | 3 | 3 |
| phenylcoumarans (B) | 8 | 8 |
| resinols (C) | 5 | 4 |
| dibenzodioxocins (D) | 1 | 1 |
| spirodienones (F) | 4 | 4 |
| α,β-diaryl ether (E) | n.d. | n.d. |
| total | 100 | 100 |
| Lignin aromatic unitsb | ||
| H (%) | 6 (14) | 3 (13) |
| G (%) | 58 (54) | 60 (56) |
| S (%) | 36 (30) | 37 (31) |
| S/G | 0.62 (0.56) | 0.62 (0.56) |
a
percentage of total lignin interunit linkage (A−F; see Supporting Information for details), n.d.: not detected
b
Molar percentages (H + G + S = 100) excluding or including (in brackets) p-coumaric acid (H) and ferulic acid (G).