Azobenzene and 2,3-dichloro-5,6-dicyanobenzoquinone donor-acceptor complexation and analysis of the magnetic anisotropy of the nitroso substituent in aromatic systems

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The first part of this thesis describes the evaluation of a new electron donor-acceptor (DA) bond between azobenzene (AB) with the electron deficient quinone 2,3-dichloro-4,5-dicyanobenzoquinone (DDQ), the former acting as an electron-donor and the latter as an electron acceptor. A novel feature of AB is that it may exist in one of two interconvertable isomer forms, cis-AB (contracted structure) and trans-AB (extended structure). Since both of these isomers have different shapes and electronic properties, my research is designed to test the binding of the cis/trans AB isomers to DDQ in solution. Another goal is to grow cocrystals of the AB isomers with DDQ for imaging these molecular aggregates in the cocrystal state by X-ray diffraction analysis. AB/DDQ association in solution is observed optically for the trans-isomer as newly formed red complexes. Concentration of the red solutions results in trans-AB/DDQ cocrystals whose X-ray diffraction structure has been determined. Attempts to cocrystallize cis-AB/DDQ complexes have been attempted, so far without success. The second part of this thesis involves experimental and computational studies of nitrosobenzenes to evaluate the dramatic anisotropic magnetic shielding effects of the nitroso group on the NMR chemical shifts of nearby nuclei. The large magnetic anisotropy gives a ∆∂ of 3.5 ppm for the syn and anti ortho 1H NMR signals and a ∆∂ of 34 ppm for the syn and anti ortho 13C NMR signals. Fifty-six proton chemical shifts in 14 nitrosobenzene structures have been calculated using B3LYP density functional theory with several different basis sets and correlated with experimental values. In addition, forty-four proton chemical shifts from a series of simple aromatic structures lacking the nitroso group (e.g. styrene, benzaldehyde, benzonitrile, and anilines) have been added to the correlation for comparison. The best linear fit of the calculated shifts to experimental values for 1H-NMR is obtained for B3LYP/6-31G*, with an rms deviation of 0.074 ppm for 1H NMR. For 13C NMR, the best linear fit is for B3LYP/DZVP2//TZVP, with an rms deviation of 3.140 ppm. By modeling NMR shifts of nitrosobenzene, we aim to better understand the basis of the large magnetic anisotropy observed for the nitroso group.

Electronic Thesis or Dissertation
Organic chemistry, Physical chemistry