Abstract:Theoretical validation and proposition of the reductive biodehalogenation pathways for aromatic halogenated compounds conducted by Dehalococcoides ethenogenes 195 were studied. Density functional theory calculations were carried out at the B3LYP/6-31G(d) level for polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and chlorobenzenes, and molecular total energy (ET) of structuraly possible daughter products were adopted as the probe of the dehalogenation reaction activity. ET could indicate the main dehalogenation daughter products of PCDD/Fs, PCBs, PBDEs and chlorobenzenes conducted by strain 195. The dehalogenation reaction favored the formation of daughter product having the lowest ET. In addition, the energy gap between a structuraly possible daughter product and the possible daughter product having the lowest ET (?ET) could be used to estimate the existence of a secondary daughter product: the smaller the ?ET, the more possible to form a secondary daughter product.