Electron affinities and reductive dechlorination of toxic polychlorinated dibenzofurans: A density functional theory study

Density functional theory studies were performed to obtain the adiabatic electron affinities of 15 polychlorinated dibenzofurans (PCDFs), including toxic PCDFs. Three-parameter hybrid density functional B3LYP, with different basis sets up to 6-311 +G(2d,2p), was utilized. All the studied PCDFs have planar structures, but some of them attain nonplanar structures upon becoming anions. The lowest unoccupied molecular orbitals of all the PCDF neutrals were found to be pi* orbitals. The singly occupied molecular orbitals of most of the anions have pi character, while the same found for the anions with longer C-Cl bonds have GF character. The present study clearly showed that chlorine atom bends as the carbon-chlorine bond stretches and the dechlorination could take place through the pi*-sigma* orbital mixing. The electron affinities of all the selected PCDFs, like those of their toxic polychlorinated dibenzo-p-dioxin and biphenyl counterparts, were positive. Interestingly, the calculated electron affinity of the most toxic 2,3,7,8-tetrachlorodibenzofuran (TCDF) is the largest among the electron affinities calculated for the eight selected TCDFs. The adiabatic electron affinities obtained at the B3LYP/6-311+G(2d,2p) level were 1.029, 1.114, 1.161, 1.286, and 1.253 eV for the toxic 2.3.7.8-TCDF, 1,2,3,7,8-PeCDF, 2,3,4,7,8-PeCDF, 1,2,3,4,7,8-HCDF, and 1,2,3,6,7,8-HCDF, respectively.