APPLICATION OF MARCUS THEORY TO GAS-PHASE SN2 REACTIONS - EXPERIMENTAL SUPPORT OF THE MARCUS THEORY ADDITIVITY POSTULATE

Through the analysis of sufficiently fast identity exchange reactions, the Marcus theory additivity postulate has been tested and verified f or two sets of gas-phase SN2 reactions: X- + RCH2Y --> XCH2R + Y- (whe re X and Y = Cl and/or Br and R = CN, C6H5). Statistical RRKM theory, within the microcanonical variational transition state (muVTS) approxi mation, is used to interpret the experimental kinetic data for each re action to estimate the activation energies relative to separated react ants. Complexation energies, determined experimentally, are used in co njunction with the data from the RRKM analysis to obtain potential sur face energetics. The Marcus expression is then used to determine wheth er the intrinsic component of the activation energy for the cross reac tion is the mean of the activation energies for the two corresponding identity exchange reactions. Good agreement is found for R = C6H5 and CN.