The 2-butyl cation in trifluoroacetic acid. A hydrogen-bridged carbonium ion

Article abstract of DOI:10.1021/ja00416a012

The solvolyses of CH₃CH₂CH(OTs)CH₃, CH₃CH₂CD(OTs)CD₃ (III) and CD₃CD₂CH(OTs)CH₃ (XIII) have been studied in CF₃COOH and CF₃COOD. The product distributions and solvolysis rates are consistent with the intermediacy of a hydrogen-bridged 2-butyl cation. The ratio of the solvolysis rates of III to XIII is 1.1-1.2 which is consistent with anchimeric assistance by a β-H on C₃. The rate of additions of CF₃COOH to 2-butene is less than half as fast as the trifluoroacetolysis, thereby eliminating 2-butene as an intermediate in the reaction. The steady-state concentration of 2-butene is shown to be proportional to added [CF₃COONa], indicating that the trifluoroacetate anion, often used as a buffer, is a strong enough base to direct the reaction toward elimination products.