Bond making kinetic isotope effect

Gives bond making kinetic isotope effect (BMKIE). For this case only, defined as kp/kH. 

Equilibrinm isotope effects are normal (>1.0) if the substrate is more stiffly bonded and inverse (<1.0) if the product is more stiffly bonded. Primary kinetic isotope effects are almost always normal, as the atom being transferred is more weakly bonded in the transition state. Isotope effects in positions not subject to bond breaking or making are secondary and are good tools for determining transition state stmctnre. They may be either normal or inverse. 

We now carry the argument over to transition state theory. Suppose that in the transition state the bond has been completely broken then the foregoing argument applies. No real transition state will exist with the bond completely broken—this does not occur until the product state—so we are considering a limiting case. With this realization of the very approximate nature of the argument, we make estimates of the maximum kinetic isotope effect. We write the Arrhenius equation for the R-H and R-D reactions... 

There is one special experimental indication of this mechanism. If the reaction is carried out in a deuterated solvent (D20 instead of H20) the rate of the reaction increases. This is a solvent isotope effect rather than a kinetic isotope effect and needs some explanation. If you examine the three examples of SAC in the previous pages you will see that they share these characteristics a fast proton exchange is followed by a rate-determining step that does not involve the making or breaking of any bonds to hydrogen. In general terms ... 

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