A Barrier-Free Atomic Radical-Molecule Reaction: F + Propene
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- 作者：Ji-Lai Li ; Cai-Yun Geng ; Xu-Ri Huang ; Chia-Chung Sun
- 刊名：Journal of Chemical Theory and Computation
- 出版年：2006
- 出版时间：November 2006
- 年：2006
- 卷：2
- 期：6
- 页码：1551 - 1564
- 全文大小：875K
- 年卷期：v.2,no.6(November 2006)
- ISSN：1549-9626
文摘
The possible reaction mechanism of atomic radical F with propene is investigatedtheoretically by a detailed potential energy surface (PES) calculation at the UMP2/6-311++G(d,p) and CCSD(T)/cc-pVTZ (single-point) levels using ab initio quantum chemistry methodsand transition-state theory. Various possible reaction paths including addition-isomerization-elimination reactions and direct H-atom abstraction reactions are considered. Among them, themost feasible pathway should be the atomic radical F (2F) attacking on the C=C double bondin propene (CH3CH=CH2) to form a weakly bound complex I1 with no barrier, followed by atomicradical F addition to the C=C double bond to form the low-lying intermediate isomer 3barrierlessly. Starting from intermediate isomer 3, the most competitive reaction pathway is thedissociation of the C2-C3 single bond via transition state TS3-P5, leading to the product P5,CH3 + CHF=CH2. However, in the direct H-atom abstraction reactions, the atomic radical Fpicking up the b-allylic hydrogen of propene barrierlessly is the most feasible pathway fromthermodynamic consideration. The other reaction pathways on the doublet PES are lesscompetitive because of thermodynamical or kinetic factors. No addition-elimination mechanismexists on the potential energy surface. Because the intermediates and transition states involvedin the major pathways are all lower than the reactants in energy, the title reaction is expectedto be rapid. Furthermore, on the basis of the analysis of the kinetics of all channels throughwhich the addition and abstraction reactions proceed, we expect that the competitive power ofreaction channels may vary with experimental conditions for the title reaction. The present studymay be helpful for probing the mechanisms of the title reaction and understanding the halogenchemistry.