Kinetic isotope effect
（重定向自Deuterium isotope effect）
_(2)1145.png")
![](/Images/godic/202501/08/SN1_vs_SN21145.png")
![ZPE energy differences and corresponding differences in the activation energies for the breaking of analogous C-H and C-D bonds](/Images/godic/202501/08/C-H_and_C-D_bond_breaking1145.png")
![The potential energy well of a tunneling reaction. The dash-red arrow shows the classical activated process, while the red arrow shows the tunneling path.[9]](/Images/godic/202501/08/Energy_Well_Model1145.png")
The kinetic isotope effect (KIE) is the change in the rate of a chemical reaction when one of the atoms in the reactants is substituted with one of its isotopes. Formally, it is the ratio of rate constants for the reactions involving the light (kL) and the heavy (kH) isotopically substituted reactants: