this invention relates to a process for preparing fluorinated c 4 to c 6 hydrocarbons by catalytically hydrogenating , in the presence of a base , at least partially halogenated olefins . this invention also relates to certain novel cyclic fluorinated c 5 and c 6 hydrocarbons prepared by the process of this invention . this invention further relates to the use of fluorinated c 4 to c 6 hydrocarbons as propellant gas or as working fluid for heat pump systems .