As depicted in Figure , a solvent medium can affect the energies of reactants and a TS by different degrees, causing the activation free energy to shift when a reaction occurs in a solution (liquid) phase. The ∆∆G ‡ solv of a reaction corresponds to the difference in the free energy of activation between a gas phase and a solution phase and is an important kinetic parameter for solution phase reactions. For example, ∆∆G ‡ solv can be directly used to estimate the ratio of a gas phase rate constant (k gas ) to a liquid phase rate constant (k liq ) as follows: k liq