Trajectory Studies of S↓(N)2 Nucleophilic Substitution. 7. F↑(-) + CH↓(3)CI → FCH↓(3) + CI↑(ˉ)

摘要

The PES(F,CI) analytic potential energy surface, developed previously, is used in a trajectory study of the F↑(-)+ CH3C1 SN2 reaction. The trajectory SN2 rate constants, as a function of reactant relative translational energy E↓(rel) and CH3CI temperature, are in good overall agreement with the experimental rate constants and those calculated using an ion-molecule capture/RRKM statistical model applied to PES(F,C1). The latter agreement exists even though the reaction dynamics is decidedly nonstatistical. For high E↓(rel) the reaction is direct. At lower E↓(rel) there is evidence for formation of an ion-molecule complex; however, its lifetime is too short for complete energy randomization to occur. The velocity scattering angle is isotropic at low E↓(rel) but becomes anisotropic with forward scattering as E↓(rel) is increased. The reaction exothermicity is primarily partitioned to product vibration, in disagreement with a previous experimental study. Energy transfer from the reactants to products is very selective. Excess reactant relative translational energy almost exclusively goes to product relative translation. Similarly, C-C1 stretch excitation goes to product vibration. For a 300 K CH3C1 rotational temperature, the total angular momentum is dominated by the reactant orbital angular momentum, which is strongly correlated with the product orbital angular momentum.