A Gaussian-2 study on the structures, energetics, and reactions of C_2H_3S~- anions

摘要

A computational study on the structures, energetics, and reactions of the C2H3S- isomers has been carried out. The computational model used is a modified version of the ab initio Gaussian-2 (G2) method. This modified model, called G2++, is designed specifically for anionic systems. Twelve C2H3S- isomers/conformers have been identified. The thioformylmethyl anion (1~-) is the most stable isomer and its Hf298 is -5.8 kJ mol~(-1). The next two most stable isomers are the thioacetyl anion (2~-) and 1-thiovinyl anion (3~-/4~-), which are 156.7 and 167.0/175.9 kJ mol~(-1) higher in energy than 1~-, respectively. A cyclic anion (12~-) is the highest in energy among the C2H3S- isomers and its Hf298 is 440.7 kJ mol-1. The G2++ proton affinities (PAs) of 1~- and thiiranyl anion (11~-) are 1446.0 and 1642.2 kJ mol~(-1), respectively, which are in excellent agreement with the experimental data. The G2++Hf298 of 11-, 198.9 kJ mol-1, is in very good agreement with the experimental value (192.2 kJ mol~(-1)), which is obtained by combining the experimental PA for 11~- and the Hf298 data for H~+ and thiirane. Other isomers/conformers identified include CH_2SCH~- (9~-/10~-), and 2-thiovinyl anion (5~-/6~-/7~-/8~-). Four anions, 2~-, 4~-, 5~-, and 11~-, can rearrange to 1~-, with barriers ranging from 40 to 117 kJ mol~(-1). Energy barriers for the ring opening processes 11~-10~- and 12~- → 7~- were calculated to be 182.2 and 5.2 kJ mol~(-1), respectively. Two other rearrangements, 8~- → 4~- and 3~-2~-, were found to have energy barriers over 180 kJ mol~(-1).