title: Competing E2 and SN2 Mechanisms for the F-+ CH3CH2I Reaction.
abstract: Anti-E2, syn-E2, inv-, and ret-SN2 reaction channels for the gas-phase reaction of F-+ CH3CH2I were characterized with a variety of electronic structure calculations. Geometrical analysis confirmed synchronous E2-type transition states for the elimination of the current reaction, instead of nonconcerted processes through E1cb-like and E1-like mechanisms. Importantly, the controversy concerning the reactant complex for anti-E2 and inv-SN2 paths has been clarified in the present work. A positive barrier of +19.2 kcal/mol for ret-SN2 shows the least feasibility to occur at room temperature. Negative activation energies (-16.9, -16.0, and -4.9 kcal/mol, respectively) for inv-SN2, anti-E2, and syn-E2 indicate that inv-SN2 and anti-E2 mechanisms significantly prevail over the eclipsed elimination. Varying the leaving group for a series of reactions F-+ CH3CH2Y (Y = F, Cl, Br, and I) leads to monotonically decreasing barriers, which relates to the gradually looser TS structures following the order F > Cl > Br > I. The reactivity of each channel nearly holds unchanged except for the perturbation between anti-E2 and inv-SN2. RRKM calculation reveals that the reaction of the fluorine ion with ethyl iodide occurs predominately via anti-E2 elimination, and the inv-SN2 pathway is suppressed, although it is energetically favored. This phenomenon indicates that, in evaluating the competition between E2 and SN2 processes, the kinetic or dynamical factors may play a significant role. By comparison with benchmark CCSD(T) energies, MP2, CAM-B3LYP, and M06 methods are recommended to perform dynamics simulations of the title reaction.
authors.affiliation: School of Chemistry and Chemical Engineering, Harbin Institute of Technology , Harbin 150001, People's Republic of China.
authors.forename: Li
authors.identifier: http://orcid.org/0000-0002-0143-3524
authors.initials: L
authors.lastname: Yang
authors.affiliation: School of Chemistry and Chemical Engineering, Harbin Institute of Technology , Harbin 150001, People's Republic of China.
authors.forename: Jiaxu
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: Jing
authors.initials: J
authors.lastname: Xie
authors.affiliation: Department of Chemistry and Biochemistry, Texas Tech University , Lubbock, Texas 79409, United States.
authors.forename: Xinyou
authors.initials: X
authors.lastname: Ma
authors.affiliation: School of Chemistry and Chemical Engineering, Harbin Institute of Technology , Harbin 150001, People's Republic of China.
authors.forename: Linyao
authors.initials: L
authors.lastname: Zhang
authors.affiliation: School of Chemistry and Chemical Engineering, Harbin Institute of Technology , Harbin 150001, People's Republic of China.
authors.forename: Chenyang
authors.initials: C
authors.lastname: Zhao
authors.affiliation: Department of Chemistry and Biochemistry, Texas Tech University , Lubbock, Texas 79409, United States.
authors.forename: William L
authors.initials: WL
authors.lastname: Hase