THEORETICAL THERMOCHEMISTRY AND KINETICS OF SOME HYDROGEN ABSTRACTION REACTIONS ON NITROGEN

In this work, the hydrogen abstraction reactions between NH3, NH2OH, NH2CN or NH(CN)OH and hydroxyl radical have been carefully investigated. First, we consider the enthalpies of formation of the molecules and the radicals involved in those reactions. We find that accurate theoretiCal resultS can be obtained with methods that use large basis sets, that introduce massively the electron correlation and that employ wave functions that are eigenstate of the S2 operator. At the kinetic point of view, we use the conventional transition state theory corrected for the tunneling effect by the Wigner's relation. The reaction rate constants and the activation energies have been calculated. OH and CN substituents increase by only a few kcal mol-1 the activation energy. The push-pull'' combination of these substituents gives very fast abstraction and shows negative temperature dependence (E(a)<0). We can classify the reaction in the decreasing order of the rate constants as: NH(CN)OH much greater than NH3 = NH2OH > NH2CN.