The three pyridazines, three naphthyridines and two azoles: effect of the position of the second heteroatom on pKaH of their eight conjugate acids.

In the present work, how the position of the second nitrogen in the conjugate acids of the three pyridazines viz., 1,2-pyridazine, 1,3-pyridazine (the pyrimidine) and 1,4-pyridazine (the pyrazine) and three naphthyridines viz., cinnoline, quinazoline and quinoxaline changes the pK_aH systematically is taken up. They decrease nearly by a factor of half each time in the class of their own. In contrast there is an increase in the pK_aH when we move from pyrazole to imidazole. The pK_aH of pyrazole is less than imidazole by −4.45 units. Suitable explanations are given. [ABSTRACT FROM AUTHOR]