Investigation of the Alcohols and Water Hydrogen Bonding Structure via Monomer Fraction Studies

The hydrogen bonding structure of alcohols and water is studied in this work using two association equations of state (cubic-plus-association (CPA); perturbed-chain statistical associating fluid theory (PC-SAFT)) and a theory connecting the relative static permittivity (RSP) with hydrogen bonding (RSP theory). The results from the two models are compared to experimental and molecular simulation data for free-site, monomer, and k-times bonded fractions, as well as for tetrahedrally bonded fractions for water. The agreement is satisfactory for alcohols but less so for water, especially when the most recent structural data for water are considered. This indicates that the four-site or roughly tetrahedral assumption incorporated for water in both approaches may be erroneous. It has been attempted to fit the RSP theory parameters to recently obtained data; such data show a rather small number of tetrahedral water molecules. These data are obtained from studies related to the water two-state theory. The results provide some insight into whether water can be assumed to be a homogeneous liquid or a two-state liquid, at least in the context of the theories (CPA, PC-SAFT, and RSP theory). The results are also discussed in the context of other theories and recent developments.