Temperature dependence of hydrogen bonding in alcohols

Quantum Cluster Equilibrium (QCE) theory is presented for liquid ethanol, benzyl alcohol and 2,2-dimethyl-3-ethyl-3-pentanol (DMEP). The cluster equilibria that dictate phase composition are determined by the rigorous techniques of quantum statistical thermodynamics in the canonical ensemble, based on the ab initio partition function. The characteristic features of the supramolecular clusters which comprise the QCE model are discussed in terms of binding energies, cooperativity and geometries. The validity of the resulting QCE model is demonstrated by comparison with experimental temperature dependent NMR hydroxyl proton chemical shifts of the liquid alcohols. The results indicate that cyclic tetramer and pentamer structures are the principal components of liquid ethanol and benzyl alcohol, whereas 2,2-dimethyl-3-ethyl-3-pentanol is built upon monomers and dimers only (C) 2000 Elsevier Science B.V. All rights reserved.