perfluoro-1-ethylbenzocycloalkenes transformed further to disubstitutedderivatives. In the case of perfluorotetralin, the reaction gave perfluoro-1,4-diethyltetralin. Perfluorobenzocyclobutene gave perfluoro-1,1- and -1,2-diethylbenzocyclobutenes in about equal quantities, and perfluoroindan- practically only perfluoro-1,1-diethylindan. To explain this orientation, the electronic and steric effects are considered