Kinetic isotope effect

The kinetic isotope effect (KIE) describes how the rate of a chemical reaction changes when an atom in the reactants is replaced with one of its isotopes, typically lighter or heavier versions (like replacing hydrogen with deuterium). Because isotopes have different masses, the bonds involving them stretch and vibrate differently, affecting how easily they break or form during reactions. As a result, reactions with lighter isotopes often proceed faster. KIE helps scientists understand reaction mechanisms and bond-breaking steps by observing these rate differences when isotopes are substituted.