Water Between Its Freezing and Boiling Points

Structural elucidation of water is so fundamental in understanding its roles as a solvent as well as a reagent in facilitating multifarious chemical reactions. The internal structure of water molecule is very “simple” to explain yet the physical and chemical properties of this liquid remains to be elusive in spite of tremendous theoretical and experimental efforts till date. Several propositions have been made in order to account for water structure, in particular its enigmatic hydrogen bonding environment that accounts for its exceptional properties. The concept of uniform distribution of tetrahedral network in water has been emerged from various experimental investigations. Water structure as equilibria of large number of clusters formed by varying number of water molecules has also been proposed based on computer simulations and Raman spectroscopy. Percolation model provides a quantitative picture of hydrogen bonding in liquids. The nature of hydrogen bond is dynamic in nature, spurring sporadic changes in its local structure, which can effectively be probed by various spectroscopic and scattering techniques. Local structure of water molecules is influenced by thermodynamic changes, most notably in temperature and density. Both computational experimental findings reveal that density plays a vital role in determining average number of hydrogen bonds a water monomer can have across wide temperature domain. More importantly, water undergoes a cascade of morphological changes upon alteration in temperature, which is still a fascinating subject for many researchers.

Keywords: Bifurcated hydrogen, Clusters, Coordination number, Density, Electrostatic interaction, Exchange repulsion, NMR, Percolation theory, Raman spectroscopy, VSEPR, Walrafen pentamers.