Kinetic deuterium isotope effects in the reactions of 4-nitrophenylnitromethane with various nitrogen bases in anisole

Abstract

Kinetic isotope effects have been determined for the reactions of 4-nitrophenylnitromethane (4-NPNM) and its deuteriated analogue with various neutral nitrogen bases in anisole solution. The reaction is a proton-transfer leading to an ion-pair. The values of the isotopic rate ratio k^H/k^D at 25°C are all large (> 18) and are attributable to tunnelling. The values for two bases containing the grouping NH C, namely tetramethylguanidine, NHC[N(CH₃)₂]₂, and N,N-diethylbenzamidine, NHC(C₆H₅) N(C₂H₅)₂, are markedly larger than those for the tertiary amines, quinuclidine and triethylamine. The reasons are discussed.