The unimolecular isomerisation of monofluorocyclopropane: a reaction with multiple fall-off characteristics?

Monofluorocyclopropane isomerises at 475 °C to give four products, cis-1-fluoropropene, trans-1-fluoropropene, 2-fluoropropene, and 3-fluoropropene; the ratios of product formation are not independent of pressure and it is shown that, using the Kassel representation, the individual fall-off curves correspond to values of the parameter s = 9, 6, 4, and 4 respectively. It is shown that although conventional RRKM theory can account satisfactorily for the difference in fall-off behaviour between the cis- and trans-1-propene yields, it cannot account for the pressure dependence of the formation of 2- and 3-fluoropropene; the latter behaviour is, however, easily understood in terms of the master-equation approach.