Potential energy surface stationary points and dynamics of the F− + CH3I double inversion mechanism. Issue 30 (20th July 2017)

• Record Type: Journal Article
• Authors: Ma, Yong-Tao; Ma, Xinyou; Li, Anyang; Guo, Hua; Yang, Li; Zhang, Jiaxu; Hase, William L.
• Is Part Of: Physical chemistry chemical physics. Volume 19:Issue 30(2017)
• Page Start: 20127
• Page End: 20136
• Publication Date: 2017-07-20
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c7cp02998e
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Direct dynamics simulations were performed to study the SN 2 double inversion mechanism SN 2-DI, with retention of configuration, for the F − + CH3 I reaction. Abstract : Direct dynamics simulations were performed to study the SN 2 double inversion mechanism SN 2-DI, with retention of configuration, for the F − + CH3 I reaction. Previous simulations identified a transition state (TS) structure, i.e. TS0, for the SN 2-DI mechanism, including a reaction path. However, intrinsic reaction coordinate (IRC) calculations from TS0 show it is a proton transfer (PT) TS connected to the F − ⋯HCH2 I SN 2 pre-reaction complex and the FH⋯CH2 I − proton transfer post-reaction complex. Inclusion of TS0 in the SN 2-DI mechanism would thus involve non-IRC atomistic dynamics. Indeed, trajectories initiated at TS0, with random ensembles of energies as assumed by RRKM theory, preferentially form the SN 2-DI products and ∼70% follow the proposed SN 2-DI pathway from TS0 to the products. In addition, the Sudden Vector Projection (SVP) method was used to identify which CH3 I vibrational mode excitations promote access to TS0 and the SN 2-DI mechanism. Results of F − + CH3 I simulations, with SVP specified mode excitations, are disappointing. With the CH3 deformations of CH3 I excited, the SN 2 single inversion mechanism is the dominant pathway. If the CH stretch modes are also excited, proton transfer dominates the reaction. SN 2-DI occurs, but with a very small probability of ∼1%. The reasons behind these results are discussed.