IS ISOMERIZATION IN HIGHLY VISCOUS SOLVENTS UNDER PRESSURE UNDERSTANDABLE WITH THE IDEA OF FREQUENCY-DEPENDENT FRICTION

Thermal Z/E isomerization of substituted N-benzylideneanilines realizes both the transition state theory regime at low pressures and the solvent fluctuation control regime at high pressures (where the rate constant k(obs) decreases with the solvent viscosity eta). The k(obs) were fitted to the Grote-Hynes theory based on the idea of frequency-dependent friction. The above-mentioned situation allows us to derive the correlation time tau(sc) of random frictional forces through solvent microscopic motions in the generalized Langevin equation. At eta greater than or similar to 10(2) Pa s, we get tau(sc) greater than or similar to 0.1 mu s, which is too long to justify the theory.