Water and its homologues: a comparison of hydrogen–bonding phenomena

Compounds of the type ROH are reviewed in terms of hydrogen–bonding interactions with special reference to R = H–, CH3– and C2H5–. The existence of hydrogen bonding in biological, climatic and cosmic processes is briefly described. In linear (open) structures of water and alcohols, the dimers have been the subject of detailed experimental and theoretical study. Cyclic forms of water and alcohols have also received considerable attention. Comparisons of cyclic and linear (open) structures of water and alcohols have led to the concept of cooperativity, by which bonding is strengthened by the formation of a second hydrogen bond within two compounds joined by an existing hydrogen bond. Complexes with other donor and acceptors are reviewed, including the simplest compound of this type, H2O...HF, for which accurate structural and thermodynamic properties have been reported. The transient chirality of the cyclic trimer of water has been recognized for some time and a particularly interesting recent paper measures the right–handed (or clockwise) and left–handed (or anticlockwise) form of the complex of water trimer with indole compounds. This has possible implications for the more recent recognition that methanol and ethanol also exist in chiral forms as cyclic trimers and possibly also as one of the forms of a cyclic tetramer. It is hoped that future work will lead to a better understanding of hydrogen bonding. A particularly important area concerns the dynamic factors controlling the very fast molecular changes that are associated with the central role of hydrogen bonding in the biological and physical processes associated with all forms of life.