take part in the reactioncoordinate. Solvent relaxation does not follow the chemical process but produces it. Again the solvent does not adjust to the changing chemical system but takes part in it. The motion of the solvent molecules themselves is an important part of the motion along the reaction coordinate. The progress in the chemical process is bound to the solvent rearrangement. Now, in the framework of these ideas, we can examine the hypothesis of equilibrium of the transition state solvation. The transition state energy is a minimum for all normal coordinates corresponding to the positive eigenvalues of the force constant matrix and a maximum for the transition vector corresponding to the negative eigenvalne. The transition state energy is a minimum only for coordinates orthogonal to the reaction coordinate. So, in the degree that solvation parameters belong to the reaction coordinate at the transition state, its energy is not a minimum respecting the solvation parameters. Consequently, a statistical average of the solvation parameters, according to Boltzmann's law, does not describe the transition state solvation. The hypothesis of equilibrium of transition state solvation is not included in the transition state theory because the separation of solute and solvent molecules at the transition state, for solvent molecules included in the reaction coordinate, is not possible. Transfer thermodynamic functions for the transition state may still be evaluated from transition state theory, but they are meaningless. It is completely erroneous to interpret transfer thermodynamic functions for the transition state in analogy with those of some stable species, assuming that the transition state is solvated in the same manner as a stable solute species having
the same structure would be. I t is rather surprising that this approach has been employed in the interpretation of kinetic data corresponding to solvolysis reaction. The role of the solvent in these reactions, as a reactant, is evident. It could be said that the ensemble of reactants plus the solvent molecules that participate in the activation process are in equilibrium with the rest of solvent, if we desire to maintain this approach. But this idea implies distinguishing between solvent-reactant mtrlecules and solven~-pnssivt~ molewlri, a disfinctiun of rather doubtiul signiticance, hecause the thermod~namir distinction between these types of molecules is not possible. The eauilibrium or noneauilibrium of transition state solvation will be a pseudoquestion in the degree that the solvation takes Dart in the reaction coordinate. The central ~roblem in each reaction is to know whether the solvation are an important part of the reaction coordinate. Literature Cited (11 Abraham,M. H..andAbrahsm.M.K . . P m a Phy8. Orf. Chem., 11.2 (19741. . J., and Brortan.T. J.. J.Amer C k e m Soc.. SO, (21 Alexander. R., KO,E. C. F., Parker. A
(9)Pr0ss.A..J. Arne,. C h e m Soe.,$8,776 (1976). Sordo,T.,Arumi,M.,andBertr&n, J., J. C h e m S o c Prrkin11,708(1981);Sordo,T., Campillo,M.,Oiivs,A.,andBertr~n,J., Chem.Phys. Leilers.SS.225 (19821.
(101
Volume 61
Number 5
May 1964
417
