Table 1 Assignments of lignin IR and ¹H-NMR spectral bands

IR wavenumber (cm⁻¹)

 3390

OH stretching in phenolic and aliphatic structures

 2933/2930

C–H vibration in –CH₃ and –CH₂–

 2850

C–H vibration in CH₃O–

 1681

Conjugated carbonyl groups

 1608

Aromatic skeleton expansion vibration

 1421

COO–vibration

 1190

Asymmetric stretching vibration of SO ²⁻₃

 1037

Assignment S=O stretching vibration

 636

C–O–C stretch stretching vibration

¹H-NMR chemical shifts (ppm)

 8.50–9.70

H in carboxylic acid

 7.25–6.80

The aromatic proton of the guaiacyl units

 6.80–6.50

aromatic protons of syringyl units

 5.50–4.00

H_α, H_β, H_γ in β-O-4′, β-5′ and β-β’structure

 4.00–3.32

H in methoxyls

 3.52–3.10

H in phenolic hydroxyl group

 2.7–2.3

DMSO

 2.3–2.1

H in aromatic acetates

 2.1–1.8

H in aliphatic acetates