This paper describes the scope and limitations of the hydrofluorination reaction in superacid HF/SbF5. On the basis of experimental studies of polyfunctional substrates’ behaviour, the dramatic effect of substitution on the superelectrophilic character of ammonium–carbenium dications was emphasized. This reaction was applied to the synthesis of novel fluorinated key building blocks. Furthermore, the hydrofluorination reaction and the discovered homodimerization/fluorination reaction were applied to the synthesis of highly valued fluorinated diamines.