CH_xO(x=1,2)与NH_y(y=0,1,2)自由基反应机理的理论计算

采用MP2方法,在6-311G**和6-311++G**基组水平上优化CH2O、CHO分别与N、NH、NH2发生吸氢反应时的过渡态结构,通过振动分析,对过渡态结构进行确认;在此基础上,应用IRC理论分析了最小能量途径(MEP)上相互作用分子间化学键的变化;采用QCISD方法在6-311++G**基组水平下对各反应驻点进行单点能量校正,计算了反应活化位垒.研究表明所有反应均以协同方式进行,从反应物CH2O与N、NH、NH2到最终产物CO、NH3,反应均放热,产物渐趋稳定;6个反应中,链式反应(1)、(5)是最容易的反应途径.通过反应途径的量子拓扑分析,发现CH2O与N、NH、NH2反应化学键的断开与形成基本上都处于过渡态(S=0)附近,CHO与N、NH、NH2反应时,键的形成和断开在过渡态之后.

Theoretical calculation on the mechanisms of radical reactions between CHxO(x=1,2) and NHy(y=0,1,2)

By the MP2 method,the fully optimized geometries of transition states in the process of the CH2O and CHO reactions to N,to NH and to NH2 respectively were calculated at the level of 6-311G＊＊ and 6-311＋＋G＊＊,and then such geometries were confirmed through vibration analysis.Changes of bond lengths of interacting molecules were analyzed along the minimum energy paths（MEP） with the IRC theory.Finally,the reaction potential barriers were figured out by computing the single point energy at the same level in the way of QCISD.It was found that the whole process of the C—H bond breaking and the N—H bond forming went in the way of concerted reactions,ranging from the reactants like CH2O and N to the final products like CO and NH3.The chain reaction（reaction（1）and（5）） was the most favorable path in all six reactions,and through topological analysis of the major critical points along the reaction pathway in the CH2O reactions to N,to NH and to NH2,we found all reactions around the transition states（S=0） that the chemical bonds forming or breaking happened after such states in the case of the three CHO reactions.