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Thermochemistry of Small Organosulfur Compounds from ab Initio Calculations

2004; American Chemical Society; Volume: 108; Issue: 52 Linguagem: Inglês

10.1021/jp046993v

1520-5215

José R. B. Gomes, Manuel A.V. Ribeiro da Silva,

Advanced Chemical Physics Studies

Gas-phase standard enthalpies of formation, S−H bond dissociation enthalpies, and gas-phase acidities, at T = 298.15 K, for a large number of small sulfur-containing molecules were calculated by means of B3LYP, CBS-Q, G3MP2B3, and G3 approaches. The computed values are compared with available experimental results for these quantities. It is shown that the DFT approach is well-suited to predict S−H bond dissociation enthalpies and gas-phase acidities but fails completely in the estimation of enthalpies of formation from atomization enthalpies. However, three selected reactions, describing the fragmentation of larger molecules into small portions, show that the combination of the enthalpies of those reactions computed at the B3LYP level and the enthalpies of formation of the smaller molecules coming from the most economic composite approach yield excellent estimates of the gas-phase enthalpy of the larger molecules.