CH_3S与CH_2SH自由基反应的密度泛函理论研究

Density functionary theory study on the radical reactions between CH_3S and CH_2SH

用量子化学从头算和密度泛函理论(DFT)对CH3S与CH2SH自由基反应进行了研究。在B3LYP/6-311+G(d,p)水平上优化了反应通道各驻点物种(反应物、中间体、过渡态和产物)的几何构型,用内禀反应坐标(IRC)计算和频率分析的方法对过渡态结构及连接性进行了验证。在QCISD(T)/6-311++G(d,p)水平上计算了各物种的单点能,并对总能量进行了零点能校正。研究结果表明,CH3S与CH2SH反应为多通道反应,有3条可能的反应通道。反应物首先通过C-S键相互作用形成链状碳-硫偶合中间体IM1,再经过裂解和脱氢气机理生成主要产物P1(CH3SH+CH2S)和次要产物P2和P3。根据势能面分析,所有反应均为吸热反应。相对于CH3S与CH2SH,各产物能量分别为(-175.2,335.5和331.5)kJ.mol-1。

A detailed theoretical survey of the potential energy surface （PES） for the reaction CH3S with CH2SH is carried out at the QCISD（t）/6-311 ＋＋G（d,p）//B3LYP/6-31 1＋G（d,p） level. The geometries, vibrational frequencies, and energies of all stationary points involved in the title reaction are calculated at the B3LYP/6-311＋G（d,p） level. More accurate energy information is provided by single-point calculations at QCISD（t）/6-31 1＋＋G（d,p） level. Relationships of reactants, intermediates, transition states and products are confirmed by the intrinsic reaction coordinate （IRC） calculations. The results show that the initial association of CH3S with CH2SH is found to be a barrierless process. Firstly it forms the energy-rich adducts IM1 through the C-S bond. Then, form the main product P1 （CH3SH＋CHzS） and the secondary products P2 and P3 via the different channels. The energies of products PI-P3 are （-175.2, 335.5 and 331.5） kJ·mol^-1 relative to those of reactants.