FTIR, FTRaman, UV–Visible and NMR spectroscopic studies on 3,3′,4,4′-tetrachloroazoxybenzene, an azoxybenzene derivative with toxic effects

Abstract

We have synthesized 3,3′,4,4′ Tetrachloroazoxybenzene (TCAOB) and, later, characterized it by using infrared, Raman, 1H, 13C NMR and UV–visible spectroscopies. The structural, topological and vibrational properties of four Cis and three Trans isomers were theoretically predicted by using the hybrid B3LYP together with the 6-31G* and 6-311++G** basis sets. The 69 normal modes of vibration for all TCAOB isomers were assigned by using the scaled quantum mechanical force field (SQMFF) procedure and their experimental vibrational spectra and normal internal coordinates. The high stabilities of all Cis and Trans isomers are supported by the π→π*, n→σ*, n→π* and π*→π* electronic transitions calculated by NBO studies while the AIM analyses reveal for the Trans forms the existence of intra-molecular C[sbnd]H⋯O hydrogen bonds, as suggested by the broad IR band observed in the higher wavenumbers region. The low gap energy for the Trans I isomer supports their higher reactivity probably due to the repulsion of the more electronegative Cl and O atoms as a consequence of their proximities. In addition, the force constants for all Cis and Trans isomers were calculated by using both levels of theory. Here, the comparisons of the predicted IR, Raman, NMR and ultraviolet–visible spectra with the corresponding experimental ones demonstrate good concordances. The existence of the N[dbnd]O groups in all TCAOB isomers support the differences in their properties, as compared with those reported for TCAB.