Kinetic isotope effect in the reaction of 4-nitrophenyl-nitromethane with pentamethylguanidine in toluene

Abstract

Kinetic isotope effects have been determined for the proton-transfer and deuteron-transfer reactions of 4-nitrophenylnitromethane with pentamethylguanidine in toluene solution. The observed value of the isotopic rate ratio k^H_f/k^D_f at 25°C is 13.7 ± 0.4. The activation enthalpies are 2.4 ± 0.3 and 4.6 ± 0.3 kcal mol^{– 1} for the proton- and deuteron-transfer respectively. The results suggest a certain degree of tunnelling.