| Abstract
| - Electronic structure methods were used to calculate the aqueous reaction energies for hydrogenolysis,dehydrochlorination, and nucleophilic substitution by OH- of 4,4‘-DDT. Thermochemical properties ΔHf°(298.15 K), S° (298.15 K, 1 bar), ΔGS (298.15 K, 1 bar) were calculated by using ab initio electronic structurecalculations, isodesmic reactions schemes, gas-phase entropy estimates, and continuum solvation models fora series of DDT type structures (p−C6H4Cl)2−CH−CCl3, (p−C6H4Cl)2−CH−CCl2•, (p−C6H4Cl)2−CH−CHCl2, (p−C6H4Cl)2−CCCl2, (p−C6H4Cl)2−CH−CCl2OH, (p−C6H4Cl)2−CH−CCl(O), and (p−C6H4Cl)2−CH−COOH. On the basis of these thermochemical estimates, the overall aqueous reaction energeticsof hydrogenolysis, dehydrochlorination, and hydrolysis of 4,4‘-DDT were estimated. The results of thisinvestigation showed that the dehydrochlorination and hydrolysis reactions have strongly favorablethermodynamics in the standard state, as well as under a wide range of pH conditions. For hydrogenolysiswith the reductant aqueous Fe(II), the thermodynamics are strongly dependent on pH, and the stability regionof the (p−C6H4Cl)2−CH−CCl2•(aq) species is a key to controlling the reactivity in hydrogenolysis. Theseresults illustrate the use of ab initio electronic structure methods to identify the potentially importantenvironmental degradation reactions by calculation of the reaction energetics of a potentially large number oforganic compounds with aqueous species in natural waters.
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