Mechanism And Kinetic Calculation On The Hydrogen Abstraction Reaction Between Radicals And CH₃NH₂

The developments of computer technologies,quantum chemistry calculation methods and various dynamic theories provide us a new way to study the transient species and their dynamic properties.Quantum chemistry calculation methods,which is based on electronic structure theory,can provide us precise information of molecule structure and energy, etc. Direct dynamic calculation methods, which is based on variational transi- tion state theory, provide us a way to perform direct dynamic calculations by using the results derived from quantum chemistry calculation.In this paper, kinetic calculation on the hydrogen abstraction reaction between three kinds of active free radicals and CH3NH2 have been studied by the quantum-mechanical calculation programs with big basis sets.In the section,we studied three reaction systems as following:H atom,CH3 radical,OH radical.We optimized the geometric configurations of reactants, transition states and products in the three reaction systems using ab initio molecule orbital theory MP2 /6-311G(D,P) method and calculated frequency to get zero point energy, the reaction path was followed from the transition state both to the reactant and the product direction by using the Intrinsic Reaction Coordinate (IRC) method.Our purpose of this study is to make clear the complex processes of hydrogen abstraction reaction and to find out the main channels,which may be the theoretical aid for the experimental scientists. In order to improve the energetics along the minimum energy path, single point calculation was carried out by using QCISD(T)theory. Then we collected the data of the stationary points and interpolate points, performed direct dynamic calculation for a series of hydrogen abstraction reactions, by using conventional transition state theory and variational transition state theory adding up small-curvature tunneling effect correction in Polyrate 8.2 program.We gained a temperature series of accurate dynamic data theoretically in a large range of temperature.The main conclusions in our work are:Hydrogen abstraction reaction between radical and CH3NH2 is explored using the QCISD(T)//MP2/6-311G(D,P) method. This reaction takes place through two channels:radical abstraction from methyl group(CH3) (Rl) and amido group(NH2) (R2).The studied result make chear:(1) The potential barrier of Rl of hydrogen abstraction reaction between H atom and CH3NH2 is 23.79kJ/mol;The power of R2 is 41.20kJ/mol. The potential barrier of Rl is about 17.41kJ/mol lower than that of R2.(2) The power of Rl is 302.8 lkJ/mol;That of R2 is 306.23kJ/mol. The power of R2 is about 3.42 kJ/mol higher than that of Rl.(3) The activation energy of Rl is 3.93 kJ/mol;That of R2 is 7.04 kJ/mol. Rl is about 3.11 kJ/mol lower than R2 DIt shows Rl is the major reaction channels. On the basis of the ab initio data, the rate constants for each channel were evaluated using canonical variational transition state theory (CVT) with the small-curvature tunneling correction (SCT) method over the wide temperature range.The kinetic calculation indicates that the calculated rate constants are in good a greement with the experimental values.Quantum tunneling efect plays an important role in each reactions, especially at low temperature range.So we can think the theories value within the scope of more wide temperature to be also authentic, this solve to have no from the theories experiment result or test which can't measurese of hard to set out nowadays up.