Perturbed Equilibria and Statistical Energy Redistribution in a Gas-Phase SN2 Reaction

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Science  06 Jun 1997:
Vol. 276, Issue 5318, pp. 1536-1538
DOI: 10.1126/science.276.5318.1536

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The relative translational energy of one set of reactants in the gas-phase equilibrium between chloride ion and chloroacetonitrile35Cl + 37ClCH2CN ⇌37Cl + 35ClCH2CN is varied without affecting the energy distribution of the other set. The steady-state ratio of ionic isotopes changes so that there is an increase in the concentration of energized reactants. The ratio provides a measure of the translational energy dependence of the rate constant for the bimolecular nucleophilic substitution (SN2) reaction. The observed energy dependence is indistinguishable from that predicted by Rice-Ramsperger-Kassel-Marcus theory, suggesting that the increased translational energy redistributes statistically in the collision complex.

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