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本文采用密度泛函理论的方法计算柴油中所含部分烷烃的碳碳键间的键裂解能,与实验数据相互印证找出精度更好的方法。并通过分析理论计算结果,总结柴油中代表烃类的断键规律。采用B3LYP、B3P86、MPWB95、B1B95方法,结合6-311++G**、6-31+G**基组对标题物进行计算研究。结果表明MPWB95和B3LYP方法均可较为准确地预测出烷烃的键裂解能。由计算各种烷烃的键裂解能(BDE)可知,含有偶数碳原子数的正构烷烃的对称性比含奇数碳原子数的对称性高,而正构烷烃在断键时是在直链中间进行断裂的,因此含有偶数碳原子数的正构烷烃的键裂解能要比相邻的含有奇数碳原子数的烷烃的键裂解能要大。随着碳原子数的增加,正构烷烃的前线轨道能级差ΔE_gap大体趋势是有略微的减小。主链碳原子数相同的异构烷烃,随着侧链碳原子数的增加,其前线轨道的ΔE_gap略有减少。含碳原子总数相同的异构烷烃的ΔE_gap略小于对应正构烷烃的ΔE_gap。
In this paper, the density functional theory method is used to calculate the bond-cleavage energy of carbon-carbon bonds in some alkanes contained in diesel oil. The experimental data confirm each other to find a better method. And by analyzing the theoretical calculation results, summarize the breaking rules of the representative hydrocarbons in diesel oil. B3LYP, B3P86, MPWB95, B1B95 method combined with 6-311 ++ G **, 6-31 + G ** basis set were used to calculate the title. The results show that both MPWB95 and B3LYP methods can predict the bond cracking energies of alkanes more accurately. From the calculation of the bond cracking energy (BDE) of various alkanes, it is known that the symmetry of n-alkanes containing even-numbered carbon atoms is higher than the symmetry of odd-numbered carbon atoms while the n-alkanes are in the middle of the straight chain So that the bond cracking energy of an n-alkane containing an even number of carbon atoms is larger than the bond cleavage energy of an adjacent alkane having an odd number of carbon atoms. As the number of carbon atoms increases, the general trend of the frontier orbital energy level difference ΔE_gap of n-alkanes decreases slightly. The isoparaffins with the same number of carbon atoms in the main chain have a slight decrease ΔE_gap in the frontier orbit as the number of carbon atoms in the side chain increases. ΔE_gap for isoparaffins with the same total number of carbon atoms is slightly less than ΔE_gap for the corresponding normal paraffins.