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运用 Gaussian98程序包中半经验的量子化学 ( AM1)方法 ,对间二甲苯系列化合物(苯环上引入不同取代基 - OH、- SH、- CN时的化合物 )的热裂解机理进行了研究 ,对设定的 8种有自由基形成的热裂解过程中的反应物、产物的全优化几何构型和反应的热力学量的计算结果表明 :无论苯环上联接的是吸电子基团还是供电子基团 ,这些化合物的热裂解键 ,都是首先从苯环上甲基碳氢键开始 ,也就是说甲基碳氢键是这类化合物最易断裂的键 ,也是热裂解的最初反应过程 ,该结论与实验结果一致 ;间二甲苯上若联有供电子取代基 ( - OH,- SH) ,反应物的热反应活性将增大 ,若联有吸电子取代基 ( - CN) ,反应物的热反应活性将减小。间二甲苯系列化合物的热反应活性的顺序为 :d1>d2 >a>d3。
The pyrolysis mechanism of the m-xylene series compounds (compounds with different substituents on the benzene ring - OH, - SH, - CN) was studied by the semi-empirical quantum chemical method (AM1) The calculation results of the total optimized geometries of the products and the thermodynamic quantities of the eight kinds of free radical-forming thermal cracking processes show that whether the benzene rings are electron-withdrawing groups or electron-donating groups Group, the thermal cracking of these compounds, are the first from the benzene ring methyl carbon hydrogen bond, that is to say methyl hydrocarbon bond is the most easily broken bonds of these compounds, but also the initial pyrolysis reaction, the The results are in good agreement with the experimental results. The thermal reactivity of the reactants will increase if there are electron-donating substituents (-OH, -SH) on m-xylene. If the electron-withdrawing substituents (- CN) Thermal reactivity will decrease. The order of the thermal reactivity of m-xylene series compounds is: d1> d2> a> d3.