Conceptual problems with empirical solvent parameters

5 CONCEPTUAL PROBLEMS WITH EMPIRICAL SOLVENT PARAMETERS 

In the basicity scales, on the other hand, complications by solvent structure are not as obvious. If restriction is to aprotic solvents, as is usual, various scales though obtained under different conditions, are roughly equivalent. There is for instance a remarkably good relationship between the DN scale (obtained in dilute dichloromethane solution, i.e., with medium effects largely excluded) and the B scale (derived from measurements performed with 0.4 M solutions of MeOD in the various solvents ). The relationship between P and B, on the other hand, separates out into families of solvents. Donor measures for protic solvents eventually are hard to assess and often are at considerable variance from one scale to another. T o rationalize the discrepancies, the concept of bulk donicity was introduced but with little success. Instead, the consideration of structure changes accompanying solvation might better help tackle the problem. 

Another problem with the interpretation of multiparameter equations such as [ 13.1.2] arises since some of the parameters used are not fully independent of one another. As to this, the trend between jf and a has already been mentioned. Similarly, the parameter displays some connection to the polarity indices. Virtually, the various parameters feature just different blends of more fundamental intermolecular forces (see below). Because of this, the interpretations of empirical solvent-reactivity correlations are often based more on intuition or preconceived opinion than on physically defined interaction mechanisms. As it 

The eoneeptual problems of die empirieal solvent parameters summarized  

Further progress would be gained if the various interaction modes could be separated by means of molecular models. This scheme is in fact taking shape in current years giving rise to a new era of tackling solvent effects as follows. 

The conceptual problems of the empirical solvent parameters summarized  

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