Peraryl-X-onium ions of nitrogen and oxygen constitute an underexploited class of organoionic species. Comparison of the syntheses of these onium salts by silyl-cation-promoted C–F activation and diazonium decomposition supports the idea that both methods share a common type of reactive intermediate. Onium ions with carboranyl counterions allowed X-ray crystallographic characterization of these salts. B97-D/Def2-TZVPP(chloroform) computational studies predicted the atropisomerism in oxonium salts analogous to that of substituted biaryls. Ion pairing of racemic atropisomeric oxonium and spirotetraarylammonium ions with enantiopure BINPHAT and BINOL allowed NMR spectral assignment of each diastereomer.