Dissociative electron transfer in polychlorinated aromatics. Reduction potentials from convolution analysis and...

Area of Science:

• Electrochemistry
• Computational Chemistry
• Environmental Chemistry

Background:

• Polychlorinated benzenes are persistent environmental pollutants.
• Understanding their reductive dechlorination is key to remediation strategies.
• Accurate prediction of reduction potentials is crucial for designing effective treatment processes.

Purpose of the Study:

• To determine formal reduction potentials for dechlorination of various polychlorinated benzenes.
• To validate computational methods for predicting redox potentials and reaction mechanisms.
• To elucidate the role of electronic structure and orbital interactions in dechlorination.

Main Methods:

• Convolution analysis of voltammetric data to obtain experimental reduction potentials.
• Quantum chemical calculations (DFT-D and CCSD(T)-F12) to compute electron affinities and C-Cl bond dissociation energies.
• Comparison of theoretical predictions with experimental data across different solvent models.

Main Results:

• Formal potentials for hexachlorobenzene, pentachloroanisole, and dichlorophenoxyacetic acids were determined.
• DFT-D calculations showed good agreement with experimental redox potentials for stepwise dechlorination mechanisms.
• High-level coupled cluster methods are necessary for concerted electron transfer/bond cleavage processes.
• Orbital mixing (π*ring and σ*C-Cl) significantly stabilizes radical anions and influences reaction pathways.

Conclusions:

• Computational chemistry, particularly DFT-D, can accurately predict dechlorination potentials when accounting for specific mechanisms.
• Orbital interactions play a critical role in the stability of intermediates and the efficiency of dechlorination.
• Understanding these factors can guide the development of improved methods for degrading persistent organic pollutants.