Calculated One- and Two-Electron Reduction Potentials and Related Molecular Descriptors for Reduction of Alkyl and Vinyl Halides in Water

• Published in: Critical reviews in environmental science and technology 2001-01, Vol.31 (2), p.175-221
• Main Authors: Totten, Lisa A., Roberts, A. Lynn
• Format: Article
• Language: English
• Subjects: anaerobic; Applied sciences; biodegradation; Biological and physicochemical phenomena; Chemical thermodynamics; Chemistry; chlorinated ethylenes; computational chemistry; density functional theory; dissociative electron transfer; Elements, mineral and organic compounds; enthalpies of formation; Exact sciences and technology; General and physical chemistry; halogenated alkanes; halogenated compounds; LFERs; Natural water pollution; Pollution; QSARs; reductive dechlorination; reductive dehalogenation; Thermodynamic properties; Water treatment and pollution
• ISSN: 1064-3389; 1547-6537
• DOI: 10.1080/20016491089208

One- and two-electron reduction potentials (E 1 and E 2 values) were calculated from published thermodynamic data for 39 halogenated C 1 and C 2 compounds, including many commonly encountered groundwater contaminants. Because reductive dehalogenation is an important pathway for their destruction under anaerobic conditions, information concerning the relevant reduction potentials may be useful for assessing the thermodynamic feasibility of a particular reaction, as well as in developing linear free energy relationships (LFERs) or other quantitative structure-activity relationships (QS ARs) that may enable prediction of rates of transformation. E 1 values were calculated assuming a stoichiometry corresponding to dissociative electron transfer, which produces a carbon-centered radical and a halide ion. E 2 values were calculated for both hydrogenolysis and reductive β-elimination reactions. Uncertainties in the thermodynamic data for the organohalides under consideration may introduce substantial uncertainty in the resulting E 1 values. Hence, relationships between calculated E1 values and various surrogate parameters were also investigated. E 1 values were correlated with lowest unoccupied molecular orbital (LUMO) energies and carbon-halogen homolytic bond dissociation energies (BDE values), which were computed via density functional theory. Correlations were also attempted between E 1 values and vertical attachment energies (VAE values), the latter representing experimental measures of the ease of reduction of a molecule to a radical anion in the gas phase. These alternate descriptors may provide a means for estimating E 1 . Additional studies will need to be undertaken to establish which descriptor best correlates with reactivity in environmental reductive dehalogenation.