Abstract: 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 AM1 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)>C₈H₉-CN(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.

Key words: carbon matrix precursor, pyrolysis mechanism, AM1 method