PURPOSE: To produce a partially fluorinated new long chain compd. useful as an intermediate of a highly heat resistant lubricant, etc., by double- decomposing a partially fluorinated long chain alkene.

CONSTITUTION: Substd. hydrocarbon having at least one double bond is brought into reaction using a tungsten-contg. catalyst and releasable ethylene or an alkene at 10-200°C optionally in the presence of an inert solvent under standard atmospheric pressure, reduced pressure or the self-pressure of a reactive mixture to obtain a substd. long chain hydrocarbon having at least one central double bond. At this time, at least one kind of alkene represented by formula I or II is used so as to cause the reaction. In the formulae I, II, Rf is a 1-18 C perfluoroalkylene; each of (m) and (n) is an integer of 1-10; X is F, H, Cl, a 1-6 C alkyl, etc.; Z is H, a 1-10 C alkyl, a 7-11 C arylalkyl, etc.; and when only one kind of compd. is used, different substituents exist at both ends of CH=CH.