Nonstatistical Reactivity in a Vibrationally Excited S_N2 Intermediate

Intramolecular Microsolvation of SN2 Transition States

“…RRKM Calculations. Activation energies were inferred from the observed rates of chloride exchange by using RRKM (Rice−Ramsperger−Kassel−Marcus) theory. − Recent theoretical and experimental evidence has questioned the validity of RRKM and related theories in some gas-phase S N 2 reactions. − Nonstatistical dynamics, however, appear to be important only for ion−molecule reactions whose intermediate complexes have very short lifetimes (less than 10−100 ps), − and the intermediates of the reactions studied here should have sufficiently long lifetimes for the RRKM analysis to give accurate activation energies.…”

On the dynamics of chemical reactions of negative ions

“…highly vibrationally excited state by means of a precursor exothermic association reaction [99]. This resulted in an at least four-fold enhancement of the branching ratio for the S N 2 reaction pathway as compared to unexcited complexes.…”

“…Similarly, excitation of the doubly degenerate C-H stretch modes in the same complex induces central barrier crossing and the formation of Br − products [98]. Craig et al created the S N 2 intermediate [CF 3 CO 2 CH 3 · · · Cl − ] * in a highly vibrationally excited state by means of a precursor exothermic association reaction[99]. This resulted in an at least four-fold enhancement of the branching ratio for the S N 2 reaction pathway as compared to unexcited complexes.…”

Translational Energy Dependence and Potential Energy Surfaces of Gas Phase SN2 and Addition−Elimination Reactions

“…More recently, work in our laboratory has revealed nonstatistical dynamics in a highly energetic S N 2 intermediate . The intermediate reactant complex [Cl·CH 3 OC(O)CF 3 ] - was generated with approximately 55 kcal mol -1 of internal energy from an exothermic carbonyl exchange reaction.…”

“…14,15 More recently, work in our laboratory has revealed nonstatistical dynamics in a highly energetic S N 2 intermediate. 27 The intermediate reactant complex [Cl‚CH 3 OC(O)CF 3 ]was generated with approximately 55 kcal mol -1 of internal energy from an exothermic carbonyl exchange reaction. When generated in this manner, the intermediate was at least four times as likely to react than the expectation based on statistical theory; there is unquestionably a dynamic bias toward energy going into the S N 2 reaction coordinate relative to the ion-molecule dissociation channel.…”