Evaluating Lignin-Rich Residues from Biochemical Ethanol Production of Wheat Straw and Olive Tree Pruning by FTIR and 2D-NMR

Table 2

Assignment of main lignin and sugars ¹³C–¹H cross signals in the HSQC spectra of lignin-rich residues from wheat straw and olive tree pruning WIS fractions.

δC/δH (ppm)	Assignment
53.7/3.42	Cβ–Hβ in phenylcoumaran substructures (C)
54.1/3.04	Cβ–Hβ in resinol substructures (B)
55.6/3.7	C–H in methoxyls (MeO)
60.1/3.4–3.7	Cγ–Hγ in β-O-4′ substructures (A)
71.4/4.75	Cα–Hα in β-O-4′ linked to a G type unit (A)
70.9/3.77–4.14	Cγ–Hγ in resinol substructures (B)
72.3/4.86	Cα–Hα in β-O-4′ linked to an S type unit (A)
83.0/4.92	Cα–Hα in spirodienone substructures (D)
84.1/4.3	Cβ–Hβ in β-O-4′ linked to a G type unit (A)
85.4/4.64	Cα–Hα in resinol substructures (B)
86.5/4.2	Cβ–Hβ in β-O-4′ linked to an S type unit (A)
87.4/5.4	Cα–Hα in phenylcoumaran substructures (C)
92.3/4.88	(1→4)-linked -D-Xylopyranosyl units ()
97.0/4.2	(1→4)-linked β-D-Xylopyranosyl units ()
102.5/4.37	(1→4)-linked β-D-Xylopyranosyl units ()
104.7/6.7	C2,6–H2,6 in S units (S)
104.0/7.31	and in tricin (T)
106.7/7.2	C2,6–H2,6 in oxidized (Cα=O) S units ()
111.0/6.99	C2–H2 in G units (G)
111.0/7.32	C2–H2 in ferulate (FA)
113.5/6.27	Cβ–Hβ in p-coumarate (PCA) and ferulate (FA)
115.2/6.7–6.9	C5–H5 in G units (G)
115.2/6.74	C3,5–H3,5 in p-hydroxyphenyl (H)
115.4/6.79	C3–H3 and C5–H5 in p-coumarate (PCA)
119.6/6.81	C6–H6 in G units (G)
123.2/7.15	C6–H6 in ferulate (FA)
128/7.17	C2,6–H2,6 in p-hydroxyphenyl (H)
129.8/7.51	C2–H2 and C6–H6 in p-coumarate (PCA)
143.8/7.49	Cα–Hα in p-coumarate (PCA) and ferulate (FA)