Reveals cyanate and azide anions as exceptionally strong hydrogen bond acceptors, indicating significant steric influences on association constants across hydroxyl donor classes.
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 Ka and enthalpies of complex formation have been determined by using the intensity of the antisymmetric vibration νa(X) of the uncomplexed anions X– . The νa(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 Ka 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.
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Góralski et al. (1994) studied this question.
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