https://doi.org/10.1351/goldbook.K03405
The effect of isotopic substitution on a
the effect of isotopic substitution in reactant A is expressed as the ratio of rate constants , where the superscripts and represent reactions in which the molecules A contain the light and heavy
and with neglect of isotopic mass on can be regarded as if it were the
rate constant
is referred to as a kinetic isotope effect
. For example, in the reaction: ![Not defined](/img/inline/K03405-1.png)
isotopes
, respectively. Within the framework of transition state theory
in which the reaction is rewritten as: ![Not defined](/img/inline/K03405-2.png)
tunnelling
and the transmission coefficient
, equilibrium constant
for an isotope exchange
reaction between the transition state
[TS]‡ and the isotopically substituted
reactant A, and calculated from their vibrational frequencies as in the case of a thermodynamic isotope effect
. Isotope effects like the above, involving a direct or indirect comparison of the rates of reaction of isotopologues
, are called 'intermolecular
', in contrast to intramolecular isotope effects
, in which a single substrate reacts to produce a non-statistical distribution of isotopomeric
product molecules.See also:
isotope effect