A Quantum and Deductive Chemical Study for All Congeners of Polybromo/Chlorodibenzo-p-dioxin and Polybromo/Chlorodibenzofuran

We have performed semiempirical quantum chemical calculations to obtain the optimized structure and the free energy (DeltaG) for all congeners (1701) of polybromo/chlorodibenzo-p-dioxins, which include all the isomers of all the homologues, and those for (3321) polybromo/chlorodibenzofurans. Then, to apply the "Quantum and Deductive Chemistry Approach" on the dioxin chemistry, we have carried out the multiple linear regression (MLR) as functions of temperature and the substituted numbers and positions of chlorine and bromine. The optimized structure of dibenzo-p-dioxin and the dibenzofuran ring is significantly influenced by the substitutions of the peri and lateral halogen atoms. The bond length between the aromatic ring and halogen atom also is influenced by the neighboring atoms. The bromine substitution at the 2 and 8 positions of dibenzofuran reduces the steric repulsion between the chlorine atoms at the 1 and 9 positions. The coefficients of the predicting equation of DeltaG derived by MLR suggest that the probabilities of chlorine elimination from the peri and lateral positions for polychlorodibenzo-p-dioxin are nearly equal.

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