Phenylpropane units-lignin, common

The concentration of ethylenic groups in lignin is more commonly expressed as the number per phenylpropane (C9) unit, per 100 phenylpropane units, or per methoxyl group. For softwood lignin the number per phenylpropane unit equals approximately the number per methoxyl group. With respect to the procedure outlined above, the following calculations apply ... 

Figure L The most common linkages between phenylpropane units in lignins. (For proportions see Table I.) (Reproduced with permission from Ref. 18. Copyright 1981 Academic Press.)...

Figure 2.10. The structure of lignin (Adler, 1977). (a) Building units of lignin, (b) Enzymatic dehydrogenation of coniferyl alcohol results in a number of resonance-stabilized phenoxyl radicals. Subsequent polymerization creates the variety of linkages between phenylpropane units that is characteristic of lignin, (c) Common substmctures and their proportions, as found in Picea abies and Betula verrucosa milled wood lignins. The proportion of individual bond types is noted beside each substructure for softwoods (S/w) and hardwoods (H/w).

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