Hydrogen isotope effect on the isomerization of peroxynitrous acid

The kinetics of isomerization of deuterium and hydrogen oxoperoxonitrate, ONOOD and ONOOH, respectively, to trioxonitrate(1-), NO3-, and a deuteron or proton have been studied. Analysis of the pH-rate profiles result in a normal equilibrium isotope effect (K-H/K-D) of 3.3. The kinetic deuterium isotope effect for the isomerization reaction is 1.6 +/- 0.2 between 5 and 55 degrees. The activation enthalpies of isomerization of ONOOD and ONOOH are identical within the error of the measurement, 86.2 +/- 0.5 and 86.5 +/- 0.5 kJ mol(-1), respectively. A secondary kinetic isotope effect of 1.6 is compatible with a mechanism of isomerization where the terminal peroxide O-atom shifts to the N-atom.