PREPARATION, NMR, AND AB-INITIO IGLO STUDY OF TRIFLUOROMETHYL-SUBSTITUTED CARBOXONIUM IONS

The preparation and study of trifluoromethyl-substituted carboxonium i ons CF3C(OH)CH3+ (2), CF3C(OCH3)CH3+ (3), CF3C(OH)OCH3+ (8), and CF3C( OCH3)(2)(+) (9) by H-1 and C-13 NMR spectroscopy under superacidic con ditions at low temperature and by ab initio molecular orbital theory a t the MP(2)(fu)/6-31G level are reported. Attempted preparation of bi s(trifluoromethyl)-substituted ions CF3C(OH)CF3+ (5) and CF3C(OCH3)CF3 + (6) by protonation and methylation, respectively, of hexafluoroaceto ne (4) were not successful under similar conditions, due to the strong ly electron-withdrawing effect of two trifluoromethyl groups on the ca rbonyl moiety.