The hydrogen bonding of alcohols, cholesterol and phenols with cyanate and azide ions

Abstract

The hydrogen bonding between ROH hydrogen bond donors (alcohols, cholesterol and phenols) and the cyanate and azide anions has been investigated in CCI₄ solution by FTIR spectroscopy. Equilibrium constants K_a and enthalpies of complex formation have been determined by using the intensity of the antisymmetric vibration ν_a(X) of the uncomplexed anions X^– . The ν_a(X) frequency shifts in the NBu₄X ⋯ HOR complexes have also been measured. The cyanate and azide anions are found to be the strongest hydrogen bond acceptors 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.