Kinetics of proton-transfer reaction between 4-nitrobenzyl-cyanide and ethoxide ion in ethanol + ether from –60 to –124°C

Abstract

The rate of the proton-transfer reaction between ethoxide ion and 4-nitrobenzyl cyanide in ethanol + ether has been determined over the temperature range –60 to –124°C, by a combination of low-temperature and stopped-flow techniques. At the lowest temperatures there are positive deviations, attributed to quantum-mechanical tunnelling. The equations for a symmetrical parabolic energy-barrier have been fitted to the results. The barrier-width for the best fit is 1.62 Å, comparable with the values found for other reactions in alcoholic media; the barrier-height is 10.7 kcal mole^–1. At the highest temperature the Arrhenius plot shows a negative deviation from linearity, attributable to the preliminary formation of an unstable complex.