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

Abstract

The preparation and study of trifluoromethyl-substituted carboxonium ions CF 3 C(OH)CH 3 + ( 2 ), CF 3 C(OCH 3 )CH 3 + ( 3 ), CF 3 C(OH)OCH 3 + ( 8 ), and CF 3 C(OCH 3 ) 2 + ( 9 ) by 1 H and 13 C 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 CF 3 C(OH)CF 3 + ( 5 ) and CF 3 C(OCH 3 )CF 3 + ( 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.