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A series of para-substituted azoxybenzenes was obtained as model compounds for the investigation on the mechanism of Wallach rearrangement. Oxidation of azobenzenes with hydrogen peroxide in acetic acid solution, provided mixtures of alfa and beta isomers. Some couples of the products were separated, using chromatography and crystallization techniques, and identifiedon the basis of their carbon NMR and mass spectra. The SCSDal-gorithm can be applied to the interpretation of the I3C-NMR spectra. Recognition of the ipso andpara carbons suffice to the identification of an isomer, hence there are no strong interactions between the azoxy group and another substituent across the aromatic ring. Fragmentation of azoxybenzenes under electron impact occurs preferentially on the oxidized side of the azoxy bridge. Relative intensities of daughter ions differentiate the ONN = a. and NNO = P isomers in most cases.
Spectroscopic and magnetic data of the compound Cu(2-qic)2 .H2O (1), where 2-qic is quinoline-2-carboxylate in the light of the known X-ray structure were studied. The geometry of CuN2O3 chromophore shows a very distorted five-coordinate stereochemistry intermediate between tetragonal pyramid and trigonal bipyramid resulting from the didentate N,O-bonded two chelate ligands and one water molecule. The crystal structure is stabilized by extended hydrogen-bonding network. Magnetic data reflect the molecular character of the compound with very weak exchange interaction (zJ' = - 0.23 cm-1), transmitted through H-bonds. The physico-chemical properties of 1 are compared with a recently reported forms 2 and 3 of identical stoichiometries Cu(quinoline-2-carboxylate)2.H2O obtained in an unusual oxidative P-dealkylation reaction. The compound 1 was prepared directly from quinaldinic acid.
Hybrid density functional theory calculations at the mPW1PW91/6-31+G(d,p) level of theory have been used to investigate the optimized structures and other molecular properties of five different series of thiosemicarbazones. The investigated compounds were obtained from acenaphthenequinone, isatin and its derivatives, and alloxan. The focus of the study is the isomerism and the NMR characterization of these thiosemicarbazones. It was found that only one isomer is expected for thiosemicarbazones and methylthiosemicarbazones, while for dimethylthiosemicarbazones, two isomers are possible. All investigated thiosemicarbazones exhibit a hydrazinic proton that is highly deshielded and resonates far downfield in the proton NMR spectra. This proton is a part of a characteristic sixmembered ring, and its NMR properties are a result of its strong, intermolecular hydrogen bond. The relationships between the calculated 1H and 13C NMR chemical shifts and various geometric parameters are reported. [...]
This review classifies and analyzes over thirty heterooligonuclear platinum clusters with a wide variety of metal frameworks, from twelve to forty-four. There are thirteen heterometals (Ge, Sn, Hg, W, Mo, Ru, Rh, Pd, Os, Ni, Cu, Ag, Au) which are the partners of platinum. The clusters mostly crystallize in monoclinic (36,4%) and triclinic (30,3%) crystal classes. Their structures are complex, with platinum most commonly preferring interstitial sites, such as the centroids of icosahedrons. There are examples of distortion isomerism. The most common ligands are CO and PPh3, and it is interesting that the mean Pt-CO and M-CO bond distances are identical at 1.84 Å. In contrast, the mean Pt-μCO and M-μCO are of values of 2.02 and 1.97 Å, respectively, while the Pt-PPh3 and M-PPh3 bond distances are 2.30 and 2.28 Å, respectively. The shortest Pt-Pt, Pt-M (non-transition) and Pt-M (transition) bond distances are 2.559(2) Å, 2.412(2) Å (M = Ge) and 2.510(2) Å (M = Ni).
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