NMR-STUDY OF PROTONATED HALOTHIOPHENES .1. H-1-NMR STUDY OF CHLOROTHIOPHENIUM IONS

Well-resolved **1H NMR signals of the cations formed from chlorothiophenes were observed in the HSO//3F or AlCl//3-HCl-CH//2Cl//2 system. Chlorothiophenes are protonated exclusively at the position adjacent to sulfur, either with or without substituents. The protonation of 2-chloro-5-methylthiophene occurs at the 5-position, and, in the HSO//3F system, the cation 5H-2-chloro-5-methylthiophenium ion thus formed undergoes an irreversible 2,5-hydrogen shift.