Kinetics and Tunneling in the Proton- and Deuteron-Transfer Reaction between 2,4,6-Trinitrotoluene and 1,8-Diazabicycloundec-7-ene in Some Aprotic Solvents

Article abstract of DOI:10.1021/j100214a031

The proton/deuteron-transfer reactions of 2,4,6-trinitrotoluene with 1,8-diazabicyclo<5.4.0>undec-7-ene in acetonitrile, 1,2-dichloroethane, and dichloromethane have been found to produce an ion pair.The reaction rates at 5-35 deg C of the proton- and deuteron-transfer reactions have been followed by a stopped-flow method.The reaction rate ratio k^H/k^D diminishes from 24.0 at 10 deg C to 18.3 at 30 deg C in acetonitrile and from 35.0 at 15 deg C to 27.1 at 30 deg C in 1,2-dichloroethane.The difference in the activation energies E_a^D - E_a^H is 2.3 and 2.1 kcal mol^-1 in acetonitrile and 1,2-dichloroethane, respectively.The ratio of Arrhenius preexponential factors is 2.5 in acetonitrile and 2.0 in 1,2-dichloroethane.All these values are greater than the semiclassical limits which can be predicted since the primary kinetic isotope effect is brought about by loss of the zero-point energy difference between C-H and C-D bond at transition state.This remarkable isotope effect, when fitted to Bell's equation, indicates that there is a considerable contribution from proton tunneling.These results are discussed in comparison with those of other proton/deuteron-transfer reactions.