A Gaussian-2 study on the structures, energetics, and reactions of C 2H 3S − anions

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A computational study on the structures, energetics, and reactions of the C 2H 3S − 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 C 2H 3S − isomers/conformers have been identified. The thioformylmethyl anion ( 1 − ) is the most stable isomer and its Δ H f298 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 C 2H 3S − isomers and its Δ H f298 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++Δ H f298 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 Δ H f298 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.