The Nature of the Critical Complex and the Effect of Changing Medium on the Rate of Reaction

The nature of a critical complex may often be related to the change of the rate of the corresponding reaction when the solvent medium is varied by altering either the electrolyte concentration or the dielectric constant. It is necessary to take into consideration the ratio of volume concentration to mole fraction, the possibility of catalytic action, even that due to an ionic charge, and the possibility that the nature of the critical complex may change with changing composition. The critical complex of the bromoacetate-thiosulfate reaction appears to be the two tangent ions. In the ammonium-cyanate reaction there may be a partial de-polarization of the tangent ions. The effect of changing dielectric constant on the solvolysis of tertiary butyl chloride indicates a rather wide separation of the ions in the critical complex.