Unified solvent polarity scale

Recent attempts to unify the polarity scales of solvents (for non-specific interactions) are of great interest in rationalizing the medium effects166. Generally, the spectroscopic properties of appropriate substances are used to check the solvating ability of solvents. 4-Nitroaniline is a useful indicator for estimating solvent polarity because it is an electron acceptor molecule which presents incomplete complexation with weak donor solvents167. 

By a quantitative structure-property relationship (QSPR) analysis of a total of 45 different empirical solvent scales and 350 solvents, the direct calculation of predicted values of solvent parameters for any scale and for any previously unmeasured solvent was possible using the CODESS A program [ie. comprehensive descriptors for structural and statistical analysis) developed by Katritzky et al. [244]. The QSPR models for each of the solvent scales were constructed using only theoretical descriptors, derived solely from the molecular solvent structure. This QSPR study enabled classification of the various solvent polarity scales and ultimately allowed a unified PCA treatment of these scales. This PCA treatment, carried out with 40 solvent scales as variables (each having 40 data points for 40 solvents as objects), allowed a rational classification and grouping... 

Katritzky, A.R., Mu, L. and Karelson, M. (1997b). QSPR Treatment of the Unified Nonspecific Solvent Polarity Scale. J.Chem.Inf.Comput.ScL, 37,756-761. 

Drago has proposed a "unified scale of solvent polarities" based on an extension of the E and C acid and base parameters discussed above. Each solvent is characterized by a parameter S and the change in some property, A%, of a probe system is given hy Ax = PS + W, where P and W are constants for Ae probe. If the probe is an acceptor (Lewis acid) in a donor solvent, then... 

A unified scale of solvent polarities, taking into account both the non-specific and specific donor acceptor interactions of these solvents with solute probes, was introduced by Drago and co-workers and shown in its mathematical form below [17] ... 

The unified scale of solvent polarities was expanded to include the very important class of polar hydrogen bonding solvents. Since these solvents are capable of undergoing both non-specific and specific donor-acceptor interactions with donor solute probes, the above equation modifies to ... 

Drago RS, Hirsch MS, Ferris DC, Chronister CW A unified scale of solvent polarities for specific and non-specific interactions. J Chem Soc Perkin Trans 2 1994, 2 219-230. 

This chapter mainly focuses on the presentation of the experimental results obtained for the molecular systems representing different types of symmetry and electronic strac-tures. Therefore in the Tables 10.3.1 and 10.3.2 (see tables at the end of the this contribution) the experimental data concerning the CT2pa a function of the solvent polarity are collected. Data are taken from the published reports, however, the presented works may not be all that have been published until the present day. In order to unify the data quoted from the original papers as well as to clearly present the interactions of the two-photon absorbing molecirles (cf Figirres 10.3.6-10.3.9) with its polar and nonpolar environment, we have adapted the well-known polarity scale, based on the empirical Solvent Polarity Parameter, Ej(30), which is defined as follows ... 

---