## inverse isotope effect

https://doi.org/10.1351/goldbook.I03142
A @K03405@ in which $$\frac{k^{\text{l}}}{k^{\text{h}}}<1$$, i.e. the heavier substrate reacts more rapidly than the lighter one, as opposed to the more usual 'normal' @I03327@, in which $$\frac{k^{\text{l}}}{k^{\text{h}}}>1$$. The @I03327@ will normally be 'normal' when the frequency differences between the isotopic @T06468@ are smaller than in the reactants. Conversely, an inverse @I03327@ can be taken as evidence for an increase in the corresponding @F02481@ on passing from the reactant to the @T06468@.
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1130 [Terms] [Paper]