Kinetic isotope effects in various solvents for the proton-transfer reactions of 4-nitrophenylnitromethane with bases

Abstract

The kinetic isotope effect for the proton-transfer reactions between 4-nitrophenylnitomethane and the bases tetramethylguanidine, tri-n-butylamine, and triethylamine is markedly dependent on the solvent; for the reaction with tetramethylguanidine in toluene, exceptionally large values are found for the rate ratio at 25°(k^H/k^D= 45 ± 2) and for the ratio of the Arrhenius A-factors (A^D/A^H= 31 ± 8), and quantum-mechanical tunnelling is used to explain them.