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采用密度泛函理论DFT方法,在B3LYP/CC-PVDZ基组水平上,优化了二叔丁基氮氧自由基(DTBN)、2,2,5,5-四甲基哌啶-1-氧自由基(TEMPO)、1,1,3,3-四甲基异吲哚-2-氧自由基(TMIO)分子的几何结构。运用前线轨道理论判断氮氧自由基的反应活性中心,得到了各氮氧自由基的分子轨道图;运用电子拓扑密度(AIM)计算得出关键点的电子密度梯度径和Laplacian量2ρ(r)等值线图,进一步分析比较了4种不同结构的氮氧自由基的反应能力。结果表明,氮氧自由基的电子离域效应使其结构相对稳定,反应活性中心为N—O键,活性大小为DTBN>c-TEMPO>b-TEMPO>TMIO,如果N—O键发生重排,N—O键发生异裂的可能性较大,生成两种带电离子;若C—N发生断裂,开环结构的DTBN最容易发生反应,闭合结构的TMIO和TEMPO不易反应。
The density functional theory (DFT) method was used to optimize the concentration of DTBN, 2,2,5,5-tetramethylpiperidine-1-oxyl Free radical (TEMPO), geometry of 1,1,1,3,3-tetramethylisoindole-2-oxyl free radical (TMIO) molecule. The frontier orbital theory was used to determine the reactive center of nitroxides and the molecular orbital diagrams of each nitroxide radical were obtained. The electron density gradient (AML) and the Laplacian quantity 2ρ (r ) Contour map, further analysis of four different structures of nitroxide free radical reaction ability. The results showed that the electron-delocalization of nitroxide radicals made the structure relatively stable, the active center was N-O bond, and the activity size was DTBN> c-TEMPO> b-TEMPO> TMIO. , The N-O bond is more likely to be split, resulting in two kinds of charged ions. If C-N breaks, DTBN of the ring-opening structure is most likely to react, and the TMIO and TEMPO of the closed structure are not easy to react.