Quantum Chemistry Research of Pyrolysis Mechanism of Carbon Matrix Precursor─ Reaction energy change, orbital energy and relative stability

Standard enthalpy change, free energy change, entropy change, the frontier orbital energy and relative stability of free radicals about the 8 types of design pyrolysis processes of the series of m-xylene compounds were calculated by the AMI method in Gaussian 98 program package. The results show that the pyrolysis process of these compounds first starts from the C-H bonds of the methyls on the benzene rings. This conclusion is in accord with the experimental result. The activity sequence of the series of m-xylene compounds is C8H9OH(d1)C8H9SH(d2 ) C8H10(a) C8H9CN(d3). At the same time, it is also proved that the frontier orbital energy difference and the relative stability of these free radicals are the same as the thermodynamics parameters, so that they can be used to the study of the pyrolysis mechanism and thermoreactive activity of this series of xylene compounds.