Azines azine-like nitrogen atoms

Like other azines with a hydroxyl group a or y to a ring nitrogen atom, 3- and 4-hydroxypyridazines exist predominantly in the oxo form in the solid state and in aqueous solution. This has been established for 3(2/f)-pyridazinone and related compounds from correlations of ultraviolet spectra of unsubstituted compounds and their 0- and iV-methyl derivatives in neutral, acid, and alkaline solution, on the basis of infrared spectra (for a summary of this aspect of tauto-merism see Volume 1, Chapter VII, Section II, K) and from the determined crystal structure of 6-oxo-l,6-dihydro-3-pyridazine-carboxamide. Here, the bond lengths and positions of hydrogen atoms clearly indicate its structure as the oxo form. Similar conclusions were reached also for 4(lJ )-pyridazinones (75) and the predominant cationic structure is represented by... 

Another class of herbicides is called tri-azines. Triazine compounds consist of a benzene-like structure with alternating nitrogen and carbon atoms in a hexagonal... 

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