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Thermochemical parameters and pK a values for chlorinated congeners of thiophenol

Altarawneh, M.ORCID: 0000-0002-2832-3886, Dar, T. and Dlugogorski, B.Z. (2012) Thermochemical parameters and pK a values for chlorinated congeners of thiophenol. Journal of Chemical & Engineering Data, 57 (6). pp. 1834-1842.

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Thermochemical parameters of the complete series of congeners of chlorinated thiophenols are derived based on the accurate chemistry model of CBS-QB3. The effect of the change in pattern and degree of chlorination has been thoroughly investigated. Optimized geometries of chlorinated thiophenol molecules exhibit to a large extent very similar geometrical features. Standard enthalpies of formation of chlorinated thiophenol and thiophenoxy radicals are calculated using isodesmic work reactions. Thermodynamic scales of H and G enable the highlighting of the most stable isomer in each homologue group. Standard entropies and heat capacities are calculated with the treatment of internal rotations of the S-H group as hindered rotors. It is found that there is a rather minor effect of changes in pattern and degree of chlorination on the calculated bond dissociation enthalpies (BDH) of the S-H bond in chlorinated thiophenols. Values of solvation energies designate that the interaction of chlorinated congeners of thiophenols with water molecules decreases with the degree of chlorination; however, no apparent dependency can be deduced with regard to the pattern of chlorination. A thermodynamic cycle was constructed to estimate pK a values based on gas phase deprotonation free energies and calculated solvation energies for chlorinated thiophenol molecules and chlorinated thiophenolate anions. Calculated pK a values are in good agreement with limited available experimental measurements.

Item Type: Journal Article
Publisher: American Chemical Society
Copyright: © 2012 American Chemical Society
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