Abstract Nitration of phenylpropiolic acid derivatives ArC≡ CX (X= CN, CO 2 Me) in HSO 3 F at− 75...− 50° C afforded mononitro compounds, for instance, mO 2 NC 6 H 4 C≡ CX. Vinyl type cations generated in HSO 3 F from methyl 3-arylpropiolates ArC+= CHCO 2 Me react along two pathways. The first among them results in formation of fluorosulfonates ArC (OSO 2 F)= CHCO 2 Me, and the second one after the attack of vinyl cation on the aryl moiety of ...