2-硝基丙烯热解反应机理和电子密度拓扑研究

Pyrolytic Reaction Mechanism of 2-Nitropropene and Its DFT Study

采用密度泛函DFT(B3LYP)方法,在6-311G**,6-311++G**以及cc-pvtz基组水平上,计算了2-硝基丙烯在热解反应过程中反应物、过渡态和中间体的几何结构,研究了各反应沿极小能量途径反应分子几何构型的变化,并通过电子密度拓扑分析,讨论了反应过程中化学键断裂、生成的变化规律.结果表明,2-硝基丙烯的热解反应存在2种反应机理,一是甲基上的H原子进攻硝基上的O原子直接生成CH2CCH2和HNO2,反应位垒为199.6 kJ/mol;二是O原子进攻亚甲基C原子首先生成四元环状中间体,位垒为200.3 kJ/mol,环状中间体进一步发生C—C键和N—O断裂生成CH3CNO和CH2O,此反应是一个一步反应,位垒为144.7 kJ/mol,所得环状中间体的分解反应机理与现有的AM1的研究结果不同.

The pyrolytic reaction mechanisms of 2-nitropropene were studied systematically by DFT（B3LYP）. The geometries of the reactant, transition states and intermediates were totally optimized at 6-311G＊＊ , 6-311＋＋G＊＊ and cc-pvtz level. The geometries change of reacting molecule and charge along the MEP（mini-energy path） were discussed. Through topological analysis of the electronic density, the topological characters of the major critical points along the reaction pathway were analyzed, the change rules of the chemical bonds were discussed. The results indicated that there were two channels in pyrolytic reaction of 2-nitropropene. One channel was H atom transferring to O atom from methyl, the potential barrier was 199.6 kJ/mol, then undergoing a dissociation to give CH2CCH2 and HNO2, the other channel was O atom transferring to C atom, producing a cyclic intermediate and the barrier was 200.3 kJ/mol, then C--C bond and O--N bond cleaved in the intermediate with potential barrier 144.7 kJ/mol. The decomposable reaction mechanism of the cyclic intermediate was different from AM1 result.