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 kHf/kDf 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.