Nitrogen content basic data

The most obvious generalization implied by the data is that several acids precipitate about one-third of the preasphaltene, and that in those cases the nitrogen content of the bases is equal to or greater than that of the original material. Thus, it seems to be a soundly based conclusion that preasphaltenes consist of 30%-35% of components that are distinctly stronger bases than water, and that a substantial part of the nitrogen is bound in structures of lower basicity. 

Nitrogen atoms of the azo bond are directly engaged in the azo-hydrazone tautomeric system and it can be expected that l4/l5N chemical shifts should reflect the changes in equilibrium. This basic idea was proposed by Berrie et al.,m who used l4N chemical shifts of NHQ/NQ atoms and calculated hydrazone contents (Table 15). They obtained naturally only one set of data measurable by double irradiation technique. The intramolecular hydrogen bond has a marked effect on <5N, as can be seen after comparison of l5NQ chemical shifts in trans-azobenzene (6 = 128), and compounds 87 and 4-hydroxyazobenzene (91)110 (Table 20). From these data it follows that the proper model compounds for tautomeric systems with intramolecular... 

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