RATES OF HYDROGEN-EXCHANGE AND KINETIC ISOTOPE EFFECTS IN THE REACTION OF PARA-NITROPHENYLNITROMETHANE WITH AMINE BASES IN TOLUENE SOLUTION - ABSENCE OF INTERNAL RETURN

Rates of loss of tritium from p‐nitrophenylnitromethane‐α‐t in toluene solution catalyzed by a series of amine bases show that hydrogen exchange in this system occurs at the same rate as ionization of the carbon acid, and that internal return is not taking place. This substantiates a previous suggestion that very large deuterium isotope effects reported for some of these reactions and attributed to extensive tunnelling were determined under conditions where the isotopic label was being lost and are therefore artifacts. This study provides isotope effects which are generally much smaller than those reported previously, but some tunnelling may still be taking place in some of these reactions. Copyright © 1990 John Wiley & Sons Ltd.