Solvent Effect on the Thermodynamics of Complex Formation with Proton Transfer from 4-Nitrophenylnitromethane to Triethylamine

In studying the thermodynamics of the formation of the 4-nitrophenylnitromethane–triethylamine ion pair in different chemical solvents within the dielectric constant interval 2.4 ≤ ε ≤ 65, an increase in the ion pair stability with an increase in the medium polarity is revealed. Account for the effect of dielectric saturation of solvent molecules through the Blok–Walker function Θ(ε) gives pK= f (Θ(ε)) (Kis the equilibrium constant of ion pair formation), which is nearly linear. The electrostatic and nonelectrostatic components of the thermodynamic parameters of the reaction are estimated. The governing role of the covalent contribution to solvents with high polarity and of the electrostatic contribution to systems with ε ≤ 4–7 is established. A linear correlation between the bathochromic shift of the band in the electronic absorption spectra of solutions of the ion pair and the logarithm of the stability constant of the complex is found.