碳前驱体热解机理的理论研究──反应能量、自由基的轨道能级及相对稳定性

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

运用Ｇａｕｓｓｉａｎ ９８程序包中的 ＡＭ１方法，通过对间二甲苯系列化合物设定的８种热裂解过程的反应能量、生成自由基的轨道能级、自由基的相对稳定性的量子化学理论计算，研究了间二甲苯系列化合物的热反应活性及热裂解机理．计算结果表明：（１）各反应物的主反应路径均是苯环上甲基Ｃ－Ｈ键首先断裂．该结论与实验结果一致；（２）各反应物之间的热反应活性由大到小顺序为： Ｃ８Ｈ９ＯＨ（ｄ１）＞Ｃ８Ｈ９ＳＨ（ｄ２）＞Ｃ８Ｈ１０（ａ）＞ Ｃ８Ｈ９ＣＮ（ｄ３）．同时亦说明，自由基前线轨道能级差及生成自由基的相对稳定性和热力学等理论参数一样，亦适合于研究间二甲苯系列反应物的热解机理和热反应活性．

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.