= 3) where the isotope effects are set as 3.0 for both endo-and exo-transition state isomers, but where the k1 and k2 are both 10 3 larger than k3 and k4 (≡ DDG195 2.677 kcal/mol). Inserting these values into eqn. 1 reduces to 0.0024/0.0008 = 3.0 and the overall isotope effect remains the same as that of the individual but unequal contributions of endo-TS and exo-TS to the reaction. This behaviour contrasts with that reported 9 for the dependence of the computed intramolecular KIE on the difference in electronic energies between the endo-TS and exo-TS, shown graphically as Figure in the original article 9 and derived from the eqn. 2 quoted there. This shows an apparent strong dependency of KIE on the relative energies (indicated as DE) of the endo-and exo-transition state isomers, with the value of KIE reducing to a limiting value of unity (1.0) when DE > ± 2 kcal/mol. At these two energy limits, the population and hence the rate for one isomer would entirely dominate and the other isomer would effectively make no contribution to the overall rate. The limiting value for KIE derived from eqn. 1 should therefore correspond to that of the dominant reaction isomer rather than to unity. To explore this difference, we have replotted the original figure 9 in two ways (Figure here); one using labels defined from scheme 4 9 and one using equation 1 as quoted in this article and labels shown in scheme 1; albeit using thermally corrected free energy (DDG ‡ ) rather than electronic energy differences. These results are shown in Figures eqn. 2 as defined from scheme 4. In Figure , the following sets of ratios for