10.1021/jp025602e.s001 Luis A. León Luis A. León Rafael Notario Rafael Notario Jairo Quijano Jairo Quijano Claudia Sánchez Claudia Sánchez Structures and Enthalpies of Formation in the Gas Phase of the Most Toxic Polychlorinated Dibenzo-<i>p</i>-dioxins. A DFT Study American Chemical Society 2002 B 3LYP levels dioxin HOMO group additivity approaches NBO charges Toxic Polychlorinated Dibenzo isodesmic reactions Gas Phase DFT Study B 3LYP enthalpie formation PCDD polychlorinated dibenzo LUMO energies 2002-06-20 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Structures_and_Enthalpies_of_Formation_in_the_Gas_Phase_of_the_Most_Toxic_Polychlorinated_Dibenzo-_i_p_i_-dioxins_A_DFT_Study/3724101 A theoretical study on the molecular and electronic structures and the enthalpies of formation of several polychlorinated dibenzo-<i>p</i>-dioxins, PCDDs, has been carried out using DFT at the B3LYP/6-31G(d) and B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) levels of theory. The calculated molecular structures are planar in all of the studied PCDDs, in agreement with the available X-ray diffraction data. NBO charges, and HOMO and LUMO energies have also been obtained and discussed. The enthalpies of formation have been calculated through isodesmic reactions, and the values obtained have been compared with the few available experimental values and with values estimated by other authors using semiempirical methods or group additivity approaches.