The thermochemical data for the five isomers/conformers of [C2H5S](-), CH3CH2S- (1), CH3CHSH- (2/3), and CH3SCH2- (4/5) have been calculated and compared with available experimental data. The structural and electronic properties of the isomers/conformers are also discussed. Contrary to its oxygen analogue, the 2-mercaptoethyl anion (HSCH2CH2-) is unstable with respect to the dissociation to HS- + C2H4 without an energy barrier. In addition, plausible elimination pathways and intramolecular rearrangements for I have also been studied. The 1,2-H-2 elimination I --> H-2 + CH2CHS- and the 1,2-HS-elimination I - HS- + C2H4 have the lowest-energy barriers (260-267 kJ mol(-1)) among the plausible elimination reactions of I under investigation. Rearrangement I --> 3 has an energy barrier of 259 kJ mol(-1) and is energetically competitive with the aforementioned 1,2-elimination reactions. On the other hand, conversion of I to 4/5 may proceed via a dissociation and recombination mechanism. The estimated energy cost for I --> 4/5 is ca. 285 kJ mol(-1).