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@.