THE HYDROGEN-BONDING OF ALCOHOLS, CHOLESTEROL AND PHENOLS WITH CYANATE AND AZIDE IONS

The hydrogen bonding between ROH hydrogen bond donors (alcohols, cholesterol and phenols) and the cyanate and azide anions has been investigated in CCl4 solution by FTIR spectroscopy. Equilibrium constants K-a and enthalpies of complex formation, have been determined by using the intensity of the antisymmetric vibration nu(a)(X) of the uncomplexed anions X(-). The nu(a)(X) frequency shifts in the NBu(4)X...HOR complexes have also been measured. The cyanate and azide anions are found to be the strongest hydrogen bond accepters ever reported. The correlations between the frequency shifts and log K-a values reveal a strong influence of steric effects on association constants. The very strong basicity of the cyanate ion allows a significant discrimination of the hydrogen bond acidity of the three classes of alcohol.