Kinetics and thermodynamics of the formation of the donor-acceptor complex of tetracyanoethylene with hexamethylbenzene in solution, by a microwave temperature-jump method

Abstract

The rate of formation of the donor-acceptor complex between tetracyanoethylene and hexamethylbenzene, in 1-chlorobutane as solvent, has been measured at –83°C by a temperature-jump method using microwave heating. Equilibrium constants have also been determined over a range of temperature. The rate constant is (1.45 ± 0.3)× 10⁸ l. mol^–1 s^–1(the uncertainty referring to the estimated limits of error). This is smaller by an order of magnitude than the calculated value for a diffusion-controlled reaction. The reason for this is discussed and it is concluded that there is possibly an energy barrier due to solvation changes. The rate constant in a solvent consisting of chlorobenzene + n-heptane (40–60 v-v) has also been determined, allowance being made for the parallel complex-formation between chlorobenzene and tetracyanoethylene; at –60°C, it was found to be (8 ± 3)× 10⁸ l. mol^–1 s^–1.