Question

ArSE2 reactions are takes
place due to​

Answer 1

As an example, I will use elimination reactions of alkyl halides.

As an example, I will use elimination reactions of alkyl halides.If a reaction shows kinetic isotope effect (in this case I use Kinetic Hydrogen Isotope effect) , it means that the rate of the reaction when deuterium is used in place of hydrogen at the reaction site will change by a significant factor. If this doesn't happen, the reaction doesn't show KHI effect.

As an example, I will use elimination reactions of alkyl halides.If a reaction shows kinetic isotope effect (in this case I use Kinetic Hydrogen Isotope effect) , it means that the rate of the reaction when deuterium is used in place of hydrogen at the reaction site will change by a significant factor. If this doesn't happen, the reaction doesn't show KHI effect.Now, what causes that significant change in rate? In this case, it is the fact that in an elimination reaction, a C-X bond and a C-H bond is broken. If the C-H bond breaks in the Rate Determining Step , then using deuterium (D) in place of hydrogen (H) will decrease the rate, as C-D bond is stronger than C-H bond. So, if a reaction doesn't show kinetic isotope effect, then it means that the breaking of the bond between a common element and the element whose isotope you use for the effect doesn't break in the RDS. This implies there is another step which is a fast step, which is not the RDS, because in a single step reaction that step itself is the RDS! So there must be multiple steps in the reaction.