Very polarisable hydrogen bonds in solutions of bases having infra-red absorption continua

Abstract

As in aqueous base solutions (BH⋯B)–(where B is CH3O–) hydrogen bonds form in alcohol solutions of CH3OK and KOH. A continuous i.r. absorption shows that a double minimum potential well is present in these hydrogen bonds and that their polarisability is extremely large. Based on the experimental results presented here and on previously developed theories the following are discussed: (1) the fluctuation of the H7O–3 group; (2) the transition of the anomalous defect proton conductivity (Grotthus mechanism) to the normal hydrodynamic mechanism with increasing concentration; (3) the processes occurring during dissociation of a base. Furthermore, the i.r. spectra of solutions of pyrrole in alcohol and of imidazole and hydroxypyridine both in water and alcohol are plotted as a function of their deprotonation by CH3OK or KOH. In addition to the symmetrical (BH⋯B)– hydrogen bonds between alcohol molecules, strongly polarisable (NH⋯N)– hydrogen bonds between pyrrole molecules and polarisable (NH⋯O)– bonds between pyrrole and alcohol are also found in the pyrrole solutions. Strongly polarisable (NH⋯N)– hydrogen bonds form in the imidazole solutions at deprotonation degrees of up to 50 %. Unsymmetrical polarisable (NH⋯O)– hydrogen bonds with the solvent molecules at degrees of deprotonation > 50 % and symmetrical (BH⋯B)– hydrogen bonds between the solvent molecules at degrees of deprotonation > 80 % are found. This is shown by the variation in the plots of the absorbance of the continuum against % deprotonation. Finally, the formation of polarisable hydrogen bonds on deprotonation of the 2-hydroxypyridine is discussed.