Table 1.
Calculated O–H bond dissociation enthalpy (BDE), electron transfer enthalpy (ETE), and radical deactivation indexes (RDI) in DPPH• and ABTS•+ assays of the lignin modeling compounds.
| Number of the Compound | Lignin Modeling Compound | BDE (kcal mol−1) | DPPH• RDI | ETE (kcal mol−1) | ABTS•+ RDI | pKa in Water b |
|---|---|---|---|---|---|---|
| 1 | guaiacol | 82.4 | 1.00 ± 0.03 | 109.0 | - | 9.93 |
| 2 | methylguaiacol | 80.3 | 1.38 ± 0.03 | 105.7 | 0.92 ± 0.03 | 10.27 |
| 3 | ethylguaiacol | 80.5 | 1.35 ± 0.04 | 106.0 | - | - |
| 4 | propylguaiacol | 80.4 | 1.53 ± 0.02 | 106.0 | 1.58 ± 0.07 | 9.85 |
| 5 | isoeugenol | 77.7 | 0.90 ± 0.09 | 105.7 | 0.67 ± 0.05 | 9.89 |
| 6 | eugenol | 81.0 | 1.72 ± 0.07 | 107.3 | 0.96 ± 0.04 | 10.15 |
| 7 | vanillin | 85.3 | 0.02 ± 0.01 | 121.4 | 0.57 ± 0.03 | 7.40 |
| 8 | acetovanillone | 85.2 | 0.03 ± 0.01 | 119.5 | 0.54 ± 0.03 | 7.81 |
| 9 | propiovanillone | 85.0 | 0.05 ± 0.01 | 118.9 | 0.45 ± 0.04 | 7.98 |
| 10 | homovanillic acid | 82.0/78.7 | 1.18 ± 0.03 | 109.1/102.0 | 1.67 ± 0.02 | 4.41/ 10.52 |
| 11 | vanillylmandelic acid | 82.5/79.0 | 0.98 ± 0.02 | 111.3/103.3 | 0.92 ± 0.02 | 3.43/ 9.93 |
| 12 | vanilglycolic acid | 86.9/83.7 | 0.08 ± 0.01 | 125.7/116.7 | 0.26 ± 0.01 | 1.60/ 7.54 |
| 13 | ferulic acid | 81.8/77.6 | 1.23 ± 0.03 | 116.8/106.0 | 2.39 ± 0.07 | 4.56/ 9.39 |
| 14 | dihydroferulic acid | 81.2/79.5 | 1.23 ± 0.06 | 107.4/103.5 | 1.39 ± 0.04 | - |
| 15 | dehydrodiisoeugenol | 81.9 | 0.67 ± 0.02 a | 109.5 | - | - |
| 16 | dehydrodieugenol | 80.1 | 2.72 ± 0.03 a | 106.3 | - | - |
| 17 | divanillin | 84.8 | n.d. c | 121.6 | 0.16 ± 0.03 | 6.16/ 10.07 |
| 18 | dipropiovanillone | 86.0 | 0.014 ± 0.01 | 122.0 | - | - |
| 19 | acetovanillonylvanillic acid | 86.5/85.6 | 0.02 ± 0.01 | 121.5/120.0 | 0.26 | - |