ABSTRACT
The way out of the above situation was found due to application of the linear free energy principle (LFER - linear free energy relationships), which had been primarily suggested by Broensted in acid-basic catalysis investigations and developed by Hammett [1, 2] in generalization of substituting agent influence on equilibrium states and rates of chemical reactions. Generally, LFER is reduced to a suggestion that any deviations from the standard free energy (thermodynamic potential) of a compound are induced by various independent perturbing factors (medium, substituting agent, temperature, etc. effects) and total value AG is obtained by summing up these independent energy contributions:
G = G 0 + f > G „ . (2-1) i = l
LFE relationships are a manifestation of the so-called extra thermodynamic relationships, suggested interaction models combined with the notions of thermodynamics. Though the LFE principle is not strongly valid from positions of thermodynamics, nevertheless, it may give useful information about actuality of the suggested interaction model and the origin of connections in it [3]. In chemistry of solutions, LFER is reduced to an assumption that a solute may interact with the medium by several mechanisms (solvation types), and final solute behavior (equilibrium constants, reaction rates, distribution, and enthalpy) is defined by the linear sum of energy effects of all mentioned interactions. The type of interactions in the medium - solute system and their significance depend on the interaction model suggested. Anyway, combined consideration of both specific and nonspecific interactions and summing up their contributions are necessitated. This summation is implemented using multiparameter linear equations of the following type:
y(AG, ln£, ...) = a0 + lap*, (2.2)
where ao is the studied value without interaction (often equal it in the gas phase; however, in the presence of this "free term" all calculation errors are also summed up); xa are effects of separate types of substrate interaction with the environment, where a is the contribution (intensity) of effects to the current process; a\ and x are solvent parameters.
