Kinetics and isotope effects ort the proton transfer reaction of 4-nitrophenylphenylcyanomethane with tetramethylguanidine in acetonitrile and benzonitrile solvents

Abstract

The kinetic deuterium isotope effect for the proton transfer reaction between 4-nitrophenylphenylcyanomethane and tetramethylguanidine, kH/kD, at 25 °C, is 10.7 in acetonitrile solvent and 12.5 in benzonitrile. The enthalpy of activation difference, [Formula: see text], in both solvents is large, 2.2 kcal mol−1, and 2.4 kcal mol−1; respectively, indicating a significant contribution from proton tunnelling to the reaction. The equilibrium constants, K, measured spectrophotometrically are large, 6000 dm3 mol−1 in acetonitrile and 2000 dm3 mol−1 in benzonitrile and in good agreement with the values calculated from the kinetic measurements.