Yang Xia, Maeda Satoshi, Ohno Koichi
Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan.
J Phys Chem A. 2005 Aug 18;109(32):7319-28. doi: 10.1021/jp052067k.
An extensive quantum chemical study of the potential energy surface (PES) for all possible isomerization and dissociation reactions of CH3CN is reported at the DFT (B3LYP/6-311++G(d,p)) and CCSD(T)/ cc-pVTZ//B3LYP/6-311++G(d,p) levels of theory. The pathways around the equilibrium structures can be discovered by the scaled hypersphere search (SHS) method, which enables us to make a global analysis of the potential energy surface for a given chemical composition in combination with a downhill-walk algorithm. Seventeen equilibrium structures and 59 interconversion transition states have been found on the singlet PES. The four lowest lying isomers with thermodynamic stability are also kinetically stable with the lowest conversion barriers of 49.69-101.53 kcal/mol at the CCSD(T)/cc-pVTZ//B3LYP/6-311++G(d,p) level, whereas three-membered-ring isomers c-CH2NCH, c-CH2CNH, and c-CHNHCH can be considered as metastable intermediates which can further convert into the low-lying chain-like isomers and higher lying acyclic isomers with the lowest conversion energies of 21.70-59.99 kcal/mol. Thirteen available dissociation channels depending on the different initial isomers have been identified. A prediction can be made for the possible mechanism explaining the migration of a hydrogen atom in competition with the CC bond dissociation. Several new energetically accessible pathways are found to be responsible for the migration of the hydrogen atom. The present results demonstrate that the SHS method is an efficient and powerful technique for global mapping of reaction pathways on PESs.
本文报道了在密度泛函理论（DFT，B3LYP/6 - 311++G(d,p)）和耦合簇单双激发理论（CCSD(T)/cc - pVTZ//B3LYP/6 - 311++G(d,p)）水平下，对CH3CN所有可能的异构化和解离反应势能面（PES）进行的广泛量子化学研究。通过缩放超球搜索（SHS）方法可以发现围绕平衡结构的路径，该方法使我们能够结合下山行走算法对给定化学成分的势能面进行全局分析。在单重态PES上发现了17个平衡结构和59个相互转换的过渡态。在CCSD(T)/cc - pVTZ//B3LYP/6 - 311++G(d,p)水平下，四个具有热力学稳定性的最低能量异构体在动力学上也是稳定的，其最低转换势垒为49.69 - 101.53 kcal/mol，而三元环异构体c - CH2NCH、c - CH2CNH和c - CHNHCH可被视为亚稳中间体，它们可以进一步转化为低能量的链状异构体和高能量的非环状异构体，最低转化能为21.70 - 59.99 kcal/mol。根据不同的初始异构体确定了13个可用的解离通道。可以对解释氢原子迁移与碳 - 碳键解离竞争的可能机制进行预测。发现了几条新的能量上可及的路径负责氢原子的迁移。目前的结果表明，SHS方法是一种用于在PES上全局绘制反应路径的高效且强大的技术。
