inverse isotope effect

https://doi.org/10.1351/goldbook.I03142
A
kinetic isotope effect
in which klkh<1, i.e. the heavier substrate reacts more rapidly than the lighter one, as opposed to the more usual 'normal'
isotope effect
, in which klkh>1. The
isotope effect
will normally be 'normal' when the frequency differences between the isotopic
transition states
are smaller than in the reactants. Conversely, an inverse
isotope effect
can be taken as evidence for an increase in the corresponding
force constants
on passing from the reactant to the
transition states
.
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1130 [Terms] [Paper]