Skip to main content
Chemistry LibreTexts

SN2 reactions

  • Page ID
    1401
  • The following are animations of gas-phase trajectories for reactants with different amounts and types of energies. The reactant energy includes a relative translational energy, Erel, between Cl- + CH3Br, and a temperature, Tvr, for the CH3Br vibrational and rotational energies.

    Select Trajectories of the Cl- + CH3Br → ClCH3 + Br- SN2 Reaction

    Cl-+ CH3Br → ClCH3 + Br -

    Nucleophilic substitution by a direct mechanism; Erel = 50 kcal/mol and Tvr = 300K

    yfwang4.gif

    Cl- + CH3Br → Cl----CH3Br → ClCH3Br + Br-

    Nucleophilic substitution by an indirect mechanism, involving the Cl----CH3 complex; Erel = 1.0 kcal/mol and Tvr = 300K

    type2-50.gif

    Cl- + CH3Br → Cl----CH3Br → ClCH3---Br-→ ClCH3+Br-

    Nucleophilic substitution by an indirect Reaction mechanism, involving both Cl----CH3Br and ClCH3---Br- complex; Erel = 1.0 kcal/mol and Tvr = 300K

    type4-200.gif

    Cl- + CH3Br → Cl- + CH3Br

    A non-reactive collision; Erel = 1.0 kcal/mol and Tvr = 300K

    type5-50.gif

    Cl-+CH3Br → Cl----CH3Br → Cl-+CH3Br

    A non-reactive collision forming the Cl----CH3Br complex, which dissociates back to reactants; Erel = 1.0 kcal/mol and Tvr = 300K.

    type6-200.gif

    Cl-+CH3Br → Cl----CH3Br → ClCH3---Br-→ Cl----CH3Br → Cl-+CH3Br

    Nucleophilic substitution by an indirect mechanism involving both the Cl----CH3Br and ClCH3---Br - complex and recrossing the transition state separating these complexes; Erel = 1.0 kcal/mol and Tvr = 300K.

    type8-200.gif

    References

    1. Wang, Yanfei, Hase, William L., and Wang, Haobin, "Trajectory studies of SN2 nucleophilic substitution. IX. Microscopic reaction pathways and kinetics for Cl + CH3Br", Journal of Chemical Physics 118, 2688 (2003)

    Contributors

    • Prof. William L. Hase (Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas)