Kinetic isotope effect and tunnelling in the reaction between 4-nitrophenylnitromethane and pentamethylguanidine in acetonitrile and toluene

Abstract

Rates and activation parameters for the proton and deuteron transfer reaction of 4-nitrophenylnitro-methane with pentamethylguanidine in acetonitrile have been determined. The isotope effect and differences in activation parameters are larger than the semiclassical limits and suggest a small but significant tunnel correction. The results are well accounted for by Bell's equation for tunnelling through a parabolic barrier. Comparison of the results for acetonitrile with previously obtained values for toluene show that there is no significant effect of the solvent polarity on the tunnel correction.