Abstract: Trimethylethylenehalonium ions were prepared from 2-fluoro-3-halo-2- methylbutanes in antimony pentafluoride-sulfur dioxide solution at-60" when the participating halogen atom was chlorine, bromine, or iodine. 1, I-Dimethylethylenehalonium ions were prepared on ionization of 1-halo-2-fluoro-2-methylpropanes in antimony pentafluoride-sulfur dioxide solution between-60 and-80" when the participating halogen ...