Theoretical Approach To the Thermochemistry and Barrier Heights of the First Steps of the Radical and Anionic-polymerization of Ethene and Formaldehyde

The gas phase enthalpies of reaction and activation for the initiation and the first propagation steps of the radical and anionic polymerizations of ethene and formaldehyde were theoretically determined by high-level ab initio calculations, using respectively H-. and H- as model initiators. To correctly describe the behavior of the anionic reactions, the hydride anion must be described by a larger basis set than the hydrogen atom. It is found that the initiation step of the radical polymerization of ethene is favored, but, conversely, the anionic initiation step is favored in the case of formaldehyde. These results agree with the experimental evidence. They also demonstrate the capacity of theoretical chemistry to describe the behavior of these reactions when a high-level methodology is used

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) NH2CN

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 (Ea> ΝΉ3 ≈ NH2OH > NH2CN