Eine semiempirische Gleichung zur Beschreibung des Lösungsmitteleinflusses auf Statik und Kinetik chemischer Reaktionen. Teil I

A model has been developed for calculating the enthalpy, entropy and free energy change associated with the creation of cavities in a liquid the size of which corresponds to the volume occupied by a solvent molecule. The molar enthalpy change H_cav equals the molar enthalpy of vaporization of the liquid, the free energy change G_cav is given by G_cav=–RT ln (V_m·p_eq/RT) (V_m=molar volume,p_eq=equilibrium vapor pressure) and is related to the standard free energy of vaporization. This relationship provides an estimate of the free energy of cavity formation required to accomodate a substrate in the liquid. It has been shown, that the free energy of solvation of a substrate can be dissected into different contributions accounting for (1) the concentration dependence of partial molar free energy quantities, (2) the formation of holes in the solvent, (3) the existence of specific, short range solute-solvent interactions and (4) the dielectric polarization of the medium. Application of this concept leads to an equation of the general form G^S–G^R=a(DN^S–DN^R)+b(AN^S–AN^R)+c(G_vp^oS–G_vp^oR), where G represents the free energy of reaction or activation,DN the donor number,AN the acceptor number and G_vp^o the standard free energy of vaporization of a solventS and a reference solventR, resp.

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Mit 3 Abbildungen