BASICITY OF THE HYDROGEN-BONDS OF FORMAMIDINES SUBSTITUTED ON THE IMINO NITROGEN ATOM

The basicity of the hydrogen bonds of formamidines 1-19 was measured by means of the formation constant K(HB) Of their complexes with p-fluorophenol and the frequency shift DELTAnu(OH) of methanol hydrogen-bonded to 1-19. The study of the nu(C=N) band shows that hydrogen bonding takes place with the imino nitrogen atom. On the hydrogen-bonding basicity scale, the formamidines appear to be more basic than the corresponding amides and pyridines, and as basic as the imidazoles. The field effect of electron-withdrawing substituents and the steric effect of bulky alkyl groups on the imino nitrogen atom markedly decrease the hydrogen-bonding basicity.