Scheme 5.

Diagram highlighting the bonding motifs and potential linkages as targets for depolymerisation (in green), % occurrence values from the literature, and bond dissociation energies for a range of commonly encountered linkages/bonding motifs in native lignins.177, 178, 179, 180, 186, 187 It is important to point out that many of these % occurrence values, although reported in the literature, are unlikely or even untenable: β‐1 moieties likely do not exceed 1–2 % of all structures (substantially lower than the 9 % reported); it is impossible to encounter 19–27 % of 5‐5‐units in any lignin (it is probably restricted to a maximum of approximately 9 % in softwoods), and; the abundance of 4‐O‐5‐linkages in softwoods is almost certainly much lower than the 4–7 % claimed.