Inhomogeneity of the chemical structure of lignins isolated from various plant tissues: H-1 and C-13 NMR study

The chemical structure of dioxane lignins isolated from the whole cotton pl ant stem (DLS), its inner part (DLIS), and the cotton plant bark (DLB) was studied by H-1 and C-13 NMR spectroscopy. It was demonstrated that DLS and DLIS are distinguished only by the degree of condensation and the number of aryl-aryl ether and ester bonds. On the contrary, the chemical structure o f DLB is markedly different from that of DLS and DLIS by the ratio of the s tructure-forming units S and C, the presence of a great amount of pyrocatec hol moieties, the content of functional groups, and the length of side chai ns.