Primary hydrogen–deuterium kinetic isotope effects in the reduction of triarylcarbonium ions by formate anion

Abstract

The rates of reduction of 16 triarylcarbonium ions to the corresponding triarylmethanes by HCO₂Na and DCO₂Na have been measured in 71.0% aqueous trifluoroacetic acid containing 2.50M-formate. Brønsted plots of log k_H and log k_D against pK_R⁺ of the carbonium ion are slightly curved with the curvature of the former being the more pronounced. The kinetic isotope effect k_H/k_D varies between 1.8 and 3.2 and shows a maximum near pK_R⁺ of –4, the first such maximum observed for a hydride transfer process.