Hydrogen bonding solvent parameters

This was averaged over the total distribution of ionic and dipolar spheres in the solution phase. Parameters in the calculations were chosen to simulate the Hg/DMSO and Ga/DMSO interfaces, since the mean-spherical approximation, used for the charge and dipole distributions in the solution, is not suited to describe hydrogen-bonded solvents. Some parameters still had to be chosen arbitrarily. It was found that the calculated capacitance depended crucially on d, the metal-solution distance. However, the capacitance was always greater for Ga than for Hg, partly because of the different electron densities on the two metals and partly because d depends on the crystallographic radius. The importance of d is specific to these models, because the solution is supposed (perhaps incorrectly see above) to begin at some distance away from the jellium edge. 

Murray, J. S., S. Ranganathan, and P. Politzer. 1991. Correlations Between the Solvent Hydrogen Bond Acceptor Parameter (3 and the Calculated Molecular Electrostatic Potential. J. Org. Chem. 56, 3734. 

Octanol is a hydrogen-bonding solvent, and thus it shows certain specificity in its ability to dissolve some components. For example, K, for phenol in hexane is only 0.11 while in octanol it is equal to 29.5. There were several attempts to rationalize solvent effects using solubility parameters [15], dielectric constant [16], and others, but none appear to be consistent. n-Octanol gives the most consistent results with other physicochemical properties and drug absorption in gastrointestinal tract. 

Murray, J.S. and Politzer, P. (1991). Correlations Between the Solvent Hydrogen-Bond-Donating Parameter a and the Calculated Molecular Surface Electrostatic Potential. J.Org.Chem., 56, 6715-6717. 

The continuum model has been applied to an experimental study of the solvent effect on the 6-chloro-2-hydroxypyridine/6-chloro-2-pyridone equilibrium in a variety of essentially non-hydrogen-bonding solvents (Beak et al., 1980). In this study, a plot of log A nh/oh) versus (e - 1)/ (2e + 1), the solvent dielectric term, yielded a linear least-squares fit with a slope of 2.5 0.2, an intercept of -1.71, and a correlation coefficient of 0.9944. This result was used to estimate the gas phase free-energy difference of 9.2 kJ mole-1, which compares favorably with the observed value of 8.8 kJ mole-1 for this system. The authors also reported that alcohol solvents are correlated fairly well in this study but that other solvents seem to be divided into two classes, those that are electron-pair donors and those that are electron-pair acceptors in a hydrogen bond. The hydrogen bonding effect is assumed to be independent from the reaction field effect and is included in the continuum model by means of the Kamlet and Taft (1976) empirical parameters. The interested reader is referred to the original paper for a detailed discussion of the method and its application. 

The solubility parameter will vary with the polarity of the solvent used. Manufacturers report the values for nonbonded, moderately, and highly hydrogen-bonded solvents. In this study parameter values in polar solvents have not been considered since the interpretation of the values with polar compounds is not the same as with hydrocarbons (8). 

Table 41-12. Solubility parameter values and hydrogen-bonded solvents ...

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