The dynamics of three-center vs. four-center dissociative reactions of vinyl-halides was investigated theoretically by Langevin molecular dynamics method in the absence and in the presence of frictional interaction between the molecules and their environment. The results show a redistribution of the vibrational energy on the bonds of vinyl-halide molecules under the effect of frictional interaction. This redistribution modifies the reaction rates of the dissociation channels. The above unexpected phenomenon is most pronounced in case of vinyl-iodide and shows a slight decrease by moving towards vinyl-fluoride. It has been shown, that the existence of friction may not guarantee statistical behaviour of the dissociation processes of these asymmetrically substituted olefins. (C) 2004 Elsevier B.V. All rights reserved.