The RS-·HSR Hydrogen Bond: Acidities of α,ω-Dithiols and Electron Affinities of Their Monoradicals

Gas-phase acidities ( ) have been measured for 1,2-ethanedithiol, 1,3-propanedithiol, and 1,4-butanedithiol, using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Adiabatic electron affinities (EAs) of the thiolate monoradicals of these compounds were assigned from electron photodetachment spectra of their corresponding thiolate monoanions, acquired using a cw-ICR. The dithiols exhibit enhanced acidities (up to 8.7 kcal/mol in ) and greater EAs (up to 6.7 kcal/mol) than analogous monothiol species. These differences are attributed to an intramolecular RS-·HSR hydrogen bond in the thiolate anion. Considerations of the RO-·HOR hydrogen bond in monoanions of α,ω-diols and in the [CH3O-·HOCH3] complex anion suggest that the RS-·HSR hydrogen bond provides up to 9 kcal/mol extra stabilization.