Preparation, NMR, and ab Initio/IGLO Study of Trifluoromethyl-Substituted Carboxonium Ions1

Abstract

The preparation and study of trifluoromethyl-substituted carboxonium ions CF3C(OH)CH3+ (2), CF3C(OCH3)CH3+ (3), CF3C(OH)OCH3+ (8), and CF3C(OCH3)2+ (9) by 1H and 13C NMR spectroscopy under superacidic conditions at low temperature and by ab initio molecular orbital theory at the MP2(fu)/6-31G* level are reported. Attempted preparation of bis(trifluoromethyl)-substituted ions CF3C(OH)CF3+ (5) and CF3C(OCH3)CF3+ (6) by protonation and methylation, respectively, of hexafluoroacetone (4) were not successful under similar conditions, due to the strongly electron-withdrawing effect of two trifluoromethyl groups on the carbonyl moiety.