CH_2SH与NO_2双自由基反应机理的理论研究

Theoretical Study on the Biradical Reaction Mechanism of CH_2SH with NO_2

在B3LYP/6-311++G(2df,p)水平上优化了标题反应驻点物种的几何构型,并在相同水平上通过频率计算和内禀反应坐标(IRC)分析对过渡态结构及连接性进行了验证.采用双水平计算方法HL//B3LYP/6-311++G(2df,p)对所有驻点及部分选择点进行了单点能校正,构建了CH2SH+NO2反应体系的单重态反应势能剖面.研究结果表明,CH2SH与NO2反应体系存在4条主要反应通道,两个自由基中的C与N首先进行单重态耦合,形成稳定的中间体HSCH2NO2(a).中间体a经过C—N键断裂和H(1)—O(2)形成过程生成主要产物P1(CH2S+trans-HONO),此过程需克服124.1kJ·mol-1的能垒.中间体a也可以经过C—N键断裂及C—O键形成转化为中间体HSCH2ONO(b),此过程的能垒高达238.34kJ·mol-1.b再经过一系列的重排异构转化得到产物P2(CH2S+cis-HONO),P3(CH2S+HNO2)和P4(SCH2OH+NO).所有通道均为放热反应,反应能分别为-150.37,-148.53,-114.42和-131.56kJ·mol-1.标题反应主通道R→a→TSa/P1→P1的表观活化能为-91.82kJ·mol-1,此通道在200～3000K温度区间内表观反应速率常数三参数表达式为kCVT/SCT=8.3×10-40T4.4exp(12789.3/T)cm3·molecule-1·s-1.

The mechanism for the reaction CH2SH with NO2 was investigated at the HL//B3LYP/6-311 ＋ ＋G（2df, p） level on single potential energy surface. All stationary points involved in the title reaction were calculated at the B3LYP/6-311 ＋ ＋G（2df, p） level. Frequency calculation and intrinsic reaction coordinate （IRC） analysis at the same level were applied to validation of the connection of transition states. The results show that CH2SH＋NO2 system has four dominating reaction channels. Firstly, CH2SH and NO2 take the carbon-to-nitrogen approach forming an adduct HSCH2NO2 （a）, followed by C--N bond rupture along with H（1）--O（2） bond formation leading to the major product P1 （CH2S＋trans-HONO）. This process with a barrier height of 124.1 kJ·mol^-l. HSCH2NO2 （a） can undergo the C--O bond formation along with C--N bond rupture to HSCH2ONO （b）, and the barrier height is exceedingly high, 238.34 kJ·mol^-1, b will take subsequent conversion and dissociation to products P2 （CH2S ＋ cis-HONO）, P3 （CH2S ＋ HNO2） and P4 （SCH2OH ＋NO）. All the channels are exothermic reactions and the reaction energy of generation is -150.37, - 148.53, - 114.42 and - 131.56 kJ·mol^-1, respectively. The channel R→a→TSa/P1→P1 is the major channel for the reaction of CH2SH with NO2. Apparent activation energy for the major channel is -91.82 kJ·mol^-1. The fitted three-parameter expression for the major channel （R→a→TSa/P1→P1）is k^CVT/SCT= 8.3 × 10^-40T4.4exp（12789.3/T） in the temperature range of 200-3000 K, in which k takes unit of cm^3·molecule^-1·s^-1.