Based on the results of CNDO and INDO quantum-chemical calculations, the possibility of a vinyl substitution (along with an addition) upon reaction of perfluoropropylene, perfluoroisobutylene, and trifluorochloroethylene with alcohols, thiols, and amines, and the absence of a similar reaction in the case of tetrafluoroethylene is explained. The calculations allow the prediction that a vinyl substitution should take place in similar reactions of 1,1-di- and trifluoroethylenes, but not with mono- and 1,2-difluoroethylenes.