Tautomeric pyridines. Part X. Effects of substituents on pyridone–hydroxypyridine equilibria and pyridone basicity
The tautomeric equilibria of dimethyl 4-hydroxypyridine-2,6-dicarboxylate, and of 3–5-diethoxycarbonyl-2-methyl, 3,5-dinitro- and 2,3,5-trichloro-4-pyridone have been investigated. Substituent groups in the α-positions affect the tautomerism much more than groups in the β-positions. The protonation behaviour of pyridones in strong acids is discussed. The base strengths of pyridones can be predicted from equation (2), and such calculated values are used to estimate for tautomeric derivatives KT values which are compared with experimental data.