Kinetic hydrogen isotope effects in the ionization of some nitroparaffins

Abstract

Values are reported for the kinetic hydrogen isotope effects for proton-transfer reactions between hydroxide ions and nitromethane, nitroethane, nitrocyclohexane and 2-nitropropane, and between 2-nitropropane and pyridine, 2, 6-lutidine and acetate ions. In conjunction with earlier work the results suggest that the isotope effect has a maximum value for proton transfers between two acid-base systems of approximately equal p K , in agreement with theoretical predictions. We have confirmed that the abstraction of a proton from 2-nitropropane by 2, 6-lutidine exhibits an abnormally high isotope effect ( k H / k D = 20), probably attributable to a considerable tunnelling correction.