Dynamic Solvent Effects on Small Barrier Isomerizations

The rate constant of a chemical reaction in solution is often a strong function of the nature of the chosen solvent. The kinetic dependence due to solvent variation is usually attributed, in terms of transition state theory, to solvent effects on the entropy and enthalpy of activation. 1 Considerable attention, however, has recently been given to how transition-state-theory (tst) can break down for reactions in the condensed phases due to dynamic solvent effects . In the language of tst, dynamic solvent effects are manifested in the quantity K which corrects the tst rate constant for non-tst effects such as solvent induced barrier recrossings. 2 Empirically, dynamic solvent effects are often invoked to explain why the rate constants of many known small-barrier isomerization reactions decrease as the solvent viscosity Ƞ is increased by varying the solvent. 3