Intrinsic acidity and basicity of 2,2,2-trifluoroethanethiol. The first experimental and theoretical study

The gas phase acidity and basicity of 2,2,2-trifluoroethanethiol (TFET), i.e., the standard Gibbs energy changes for the following two reactions have been determined by means of Fourier transform ion cyclotron resonance spectroscopy: CF3CH2SH(g)--> CF3CH2S-(g) + K+(g) and CF3CH2SH2+ (g) --> CF3CH2SH(g) + H+(g). Also determined were the equilibrium constants for the 1:1 associations in dilute solution between TFET and pyridine N-oxide, 3,4-dinitrophenol (both in cyclohexane), and molecular iodine (in tetrachloromethane). Quantum-mechanical treatments at the G2(MP2) level were carried out on TFET, 2,2,2-trifluoroethanol 1, ethanethiol, and ethanol as neutral, protonated, and deprotonated species. Topological analyses of the charge densities and the Laplacians thereof were performed on all of them. This combination of experimental and theoretical information leads to a vastly enlarged view of structural effects on the reactivity of alcohols and thiols as well as to a satisfactory rationalization of the reactivity of TFET.