AbstractThe effect of pressure on the rate and equilibrium constants for the dimerization reaction of 2,4,6‐trimethylnitrosobenzene in acetonitrile was studied up to 196 MPa at 25°C in order to examine whether the dynamical effect on the reaction process in solution can be neglected as assumed in the transition state theory. All the rate constants relevant to the dimerization were determined by the pressure relaxation method. The configurational reaction volume for the dimerization and the activation volume for the dissociation were —17.4 ± 0.7 and + 5.1 ± 0.3 cm3mol1at 98 MPa, respectively. The experimental results were in reasonable agreement with the theoretical ones that were calculated for the model system composed of hard spheres according to the liquid theory and the transition state theory. The dynamical effect on the activation volume was not detected in the present reaction