硝基甲烷异构化反应势能面的ab initio研究

Ab initio Study of the CH_3NO_2 Rearrangement Potential Energy Surface

在B3LYP/ 6 311++G(2d ,2p)水平上 ,优化得到硝基甲烷CH3 NO2 的 10种异构体和 2 3个异构化反应过渡态 ,并用G2MP2方法进行了单点能计算 .根据计算得到的G2MP2相对能量 ,探讨了CH3 NO2 势能面上异构化反应的微观机理 .研究表明 ,反应初始阶段的CH3 NO2 异构化过程具有较高的能垒 ,其中CH3 NO2 的两个主要异构化反应通道 ,即CH3 NO2 →CH3 ONO和CH3 NO2 →CH2 N(O)OH的活化能分别为 2 70 .3和 2 6 7.8kJ/mol,均高于CH3 NO2的C -N键离解能 .因而 ,从动力学角度考虑 ,CH3 NO2 的异构化反应较为不利 .

The potential energy surface of rutromethane (CH3NO2), including 10 CH3NO2 isomers and 23 interconversion transition states, is probed theoretically at G2MP2//B3LYP/6-311 ++ G ( 2d, 2p) level of theory. The geometries and relative energies for various stationary points are determined. Based on the calculated G2MP2 potential energy surface, the possible nitromethane isomerization mechanism is discussed. The results are shown that the energy order for these 10 CH3NO2 isomers is IS6 > IS5 > IS3 > IS8 > IS2 > CH3NO2 > IS4 > IS10 > IS9 > IS7. The energy of IS7b HC (O) N( H) OH) is the lowest, 111.7 kJ/mol below the nitromethane ( CH,NO,), while the energy of IS6C HCN(OH)(2)) is the highest, 240.6 kJ/mol above the nitromethane ( CH,NO,). It is shown that CH3NO2 isomerizations at the initial reaction stages are of high activation barriers. Among them, the respective nitromethane-->methyl nitrite and nitromethane-->aci-nitromethane barriers are 270.0 and 267.5 kJ/mol, higher than the C - N bond dissociation energy for CH3NO2. Our results suggest that nitromethane isomerization pathways are kinetically disfavored.