A COMPARISON OF NONSPECIFIC SOLVENT EFFECTS SCALES:

ADAM CG, PM MANCINI, GG FORTUNATO, LR VOTTERO

Septembre 30-October 5.

Conferencia; 9th Latin Conference on Physical Organic Chemistry..; 2007

CLAFCO

The active role of solvents in physicochemical processes in solution has long been recognized. Different solvatochromic empirical scales are aimed at describing and quantifying the nonspecific solvation interactions at a molecular level. This work presents a new insight into the comparison of the famous ETN(30) (Dimroth-Reichardt) and ?Î* (Kamlet, Abboud and Taft, KAT) solvatochromic scales for 55 pure molecular solvents. These scales were tested against the theorethical energy for the first pi,pi* electron transition of the 4-nitroanisole EpNA (Matyushov et al.). In each case we centered the attention on the analysis of  the degree of agreement between paired values quantified through both solvent scales by applying the methodology described by J. M. Bland and D. G. Altman (B-A). In addition, the linear correlations are assessed. The B-A results and the linear correlation data are presented in the table: the bias is the average of the differences between the values quantified through both scales and the limits of agreement are computed from the equation AL=Bias?}1.96?~SD (in which SD is the standard deviation of the bias).   Difference vs average     Linear correlation     Number of solvents Bias (SD) 95% Limits of agreement r2 (SD) r   ?Î* vs ETN 0.258 (0.260) -0.251 / 0.768 0.288 (0.257) 0.537 55   ?Î*theor vs ETNtheor -0.015 (0.246) -0.497 / 0.467 0.513 (0.231) 0.716 55   ETN vs ETNtheor 0.069 (0.178) -0.044 (0.104) -0.280 / 0.418 -0.208 / 0.199 0.316 (0.178) 0.586(0.096) 0.562 0.766 55 44   ?Î* vs ?Î*theor 0.342 (0.167) 0.352 (0.185) 0.015 / 0.669 -0.015/0.714 0.744 (0.154) 0.727 (0.171) 0.863 0.853 55 44 The study reveals that the experimental values, in general, do not agree with the theoretical ones. These results were related with the contributions of induction, dispersion and dipole-dipole solvent forces to the overall solvent effect. It is expected that the results will be contribute to the evaluation of the ability of the microscopic scales to describe the nonspecific solute-solvent interactions.