THE ORTHO EFFECT IN PYRIDINES .12. SUBSTITUENT EFFECTS ON BASICITY OF 3-SUBSTITUTED 2-AMINOPYRIDINES AND 4-AMINOPYRIDINES

The basicities of 25 3-substituted 2- and 4-aminopyridines were investigated. The results are compared with each other and with data from two previously-studied series. In general, the overall substituent effect is sensitive to the distance of both the R and the NH2 groups from the ring nitrogen atom. The field/inductive-resonance composition of the interaction between the substituent and the reaction site depends on the possibility of conjugation of the exocyclic groups with the pyridine ring. The influence of tautomeric equilibria and the hydration effect are discussed.