Structures and energetics of C 3H 6S + [rad] isomers: a Gaussian-3 ab initio study

Abstract

Twenty-two isomers/conformers of C 3H 6S + radical cations have been identified and their heats of formation (Δ H f) at 0 and 298 K have been calculated using the Gaussian-3 (G3) method. Seven of these isomers are known and their Δ H f data are available in the literature for comparison. The least energy isomer is found to be the thioacetone radical cation ( 4 +) with C 2 v symmetry. In contrast, the least energy C 3H 6O + isomer is the 1-propen-2-ol radical cation. The G3 Δ H f298 of 4 + is calculated to be 859.4 kJ mol −1, ca. 38 kJ mol −1 higher than the literature value, ≤821 kJ mol −1. For allyl mercaptan radical cation ( 7 +), the G3 Δ H f298 is calculated to be 927.8 kJ mol −1, also not in good agreement with the experimental estimate, 956 kJ mol −1. Upon examining the experimental data and carrying out further calculations, it is shown that the G3 Δ H f298 values for 4 + and 7 + should be more reliable than the compiled values. For the five remaining cations with available experimental thermal data, the agreement between the experimental and G3 results ranges from fair to excellent. Cation CH 3CHSCH 2 + ( 10 +) has the least energy among the eleven distonic radical cations identified. Their Δ H f298 values range from 918 to 1151 kJ mol −1. Nevertheless, only one of them, CH 2SCH 2CH 2 + ( 12 +), has been observed. Its G3 Δ H f298 value is 980.9 kJ mol −1, in fair agreement with the experimental result, 990 kJ mol −1. A couple of reactions involving C 3H 6S + isomers CH 2SCH 2CH 2 + ( 12 +) and trimethylene sulfide radical cation ( 13 +) have also been studied with the G3 method and the results are consistent with experimental findings.