Table 4 summarizes the main characteristics. Aromatic
OCH3 (entry 2, Table 3) reflects the ratio S/G of the lignins and the
decrease trend (mimosa > willow > giant reed > silver grass) is in
accordance with the NO results (Table 4). Alkyl–aryl ether struc-
tures ( O 4) are the main linkage identified, although chemical
shift in NMR spectra attributed to C˛, Cˇ or C in these structures
have always interference of carbons from other environments.
Hence, the approach to overcome this difficulty is to subtract the
entry 1 to the entry 6 (Table 3) (Costa et al., 2014) to estimate the
total O 4 content (Table 4).