PATHWAYS OF FORMATION OF XENOBIOTICS OF THE DIOXIN TYPE - QUANTUM-CHEMICAL CONSIDERATION .2. 1,2-KETOCARBENES AS INTERMEDIATES IN THE CONVERSIONS OF POLYCHLOROPHENOLS TO DIOXIN

The AM1 method was used to calculate the enthalpies of formation of polychlorinated 1,2-ketocarbenes (PCKC) from polychlorophenols (PCP) according to a two-step scheme - deprotonation with the formation of polychlorophenolate anions (PCPA, DELTAH-1) and dechlorination to PCKC (DELTAH-2). It was shown that the biradical state of PCKC has a lower energy than the singlet state. The influence of the solvent on DELTAH-1 and DELTAH-2 was estimated within the framework of the solvation model. It was shown that DELTAH-1 decreases with increasing number of Cl atoms in PCP, which is evidence of an increase in the acidity, whereas DELTAH-2 increases, which is due to an increase in the relative stability of PCPA with increasing number of Cl atoms. A calculation of the dimerization of PCKC in the singlet state showed that this process occurs with virtually no activation energy. The electronic state of 1,2-ketocarbene and its analogs in the singlet state was studied by a nonempirical MO LCAO SCF method. A comparison with 1,2-thioketocarbene and its analogs was performed.