几种氮氧自由基结构和性质的理论计算

Theoretical Calculation on the Structure and Property of Several Nitroxides

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。

Using DFT（B3LYP） method,the two sub-butyl nitrogen oxygen free radicals（DTBN）,2,2,5,5-four methyl piperidine-1-oxygen free radicals（TEMPO）,methyl isopropyl 1,1,3,3-four indoles-2-oxygen free radicals（TMIO） molecular were completely optimized at the level of the CC-PVDZ.Using the frontier orbital theory judgment the reaction activity center of different nitroxides.And got the graph of molecular orbit of nitroxides.Using electronic topology density（AIM）,calculated the key points of electronic density gradient size and ▽2 ρ Laplacian quantity（r） isoline,further analysis compares four different structure of the nitrogen oxygen free radical response capacity.The results showed that the delocal effect of electronic made nitroxides relative stability.Compared the activity of N—O,it is DTBNc-TEMPOb-TEMPOTMIO.If N—O key occur rearrangement,the key of N—O more probably generated two different crack of charged ions.If C—N ruptures,DTBN is the most easily reactant.And TMIO and TEMPO have closed ring structures,they are not easy to open loop.