Polarisability-dipolarity

MEASUREMENTS OF H-BOND ACIDITY, BASICITY AND POLARISABILITY-DIPOLARITY BY HPLC 

The importance of H-bond acidity, basicity and polarisability-dipolarity in describing various partition processes and solubility 

Using the measured CHI data of the model compounds we can set up a correlation equation to express the H-bond acidity (a), H-bond basicity (f) and the polarisability-dipolarity (n) parameters by the CHI values obtained on a particular stationary phase with a particular mobile phase. The plot of the database descriptors as a function of the estimated ones based on the measured CHI values can be seen in Figs. 12.20-12.22. The best equations for the estimation of the descriptors are also shown in the figures. It can be seen that the CHI values obtained on Luna C-18 columns with acetonitrile and trifluoroethanol gradients are used for the fi and the ir calculations. The CHI values 

Using a solver technique (we have used the solver add-in in Microsoft Excel 6.0 ), one can calculate the 3 molecular descriptors (H-bond acidity, H-bond basicity and polarisability-dipolarity). Plass et al. 1122] published the molecular descriptors of tripeptide derivatives based on the above-described method. Although reasonably sensible data were obtained, the method has not yet been validated on a large number of 

The power of the solvation equation approach is that it can characterise various partition systems and lipophilicity scales by five molecular descriptors (dispersivity, size, polarisability-dipolarity, H-bond acidity and basicity). All of the five descriptors should be included into the linear regression equations by definition. When one or two coefficients are not significantly different from zero, it means that that particular property does not play a significant role in the partition. 

While this theory holds for ionic liquids in general when compared to organic solvents, it cannot be efficiently used to select the best ionic liquid from a pool of ionic liquids. This has been attributed to the fact that ionic liquids feature very similar Jt -values, which determine polarisability/dipolarity. 

Kirkwood took a more rigorous statistical-mechanical approach in an attempt to incorporate the effect of local ordering. His theory is only valid for rigid dipoles, and it was left to Frohlich to extend the treatment properly to a system of polarisable dipolar molecules. The work is well described in Frohlich s classic text (1949). The final outcome was the following formula, 

These criteria can be met by the "design" and synthesis of polariseable dipolar molecules. As indicated above, incorporation of a chiral centre and separation and purification of the enantiomers can afford non-centrosymmetric crystals which may exhibit SHG. 

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