Specific features of the photolytic transformations of the polynuclear quinone-aliphatic hydrocarbon systems

Dependence of the quantum yield of decomposition of quinone on the intensity of the absorbed irradiation in the compositions of 1,2-naphthoquinone, 9,10-phenanthrenequinone, and 4-nitro-9,10-phenathrenequinone with nonane has the extremal character.     

Features of photolytic transformations of di-<Emphasis Type="Italic">o</Emphasis>-quinones containing sulfide fragments

Quantum yields and products of photolytic transformation of bis(2,5-di-tert-butylcyclohexadiene-1,5-dion-3,4-yl)sulfide and 1,4,7,10-tetra-tert-butyl-5,6,11,12-tetrathia-dibenzo-cyclooctene-2,3,8,9-tetraone dissolved in saturated hydrocarbon at the action of irradiation with wavelength 436 and 313 nm, respectively. Possible mechanism of these photo reactions is proposed.     

Formation of color centers and paramagnetic species upon reduction of poly(diphenylene phthalide) with metallic lithium in DMF

Reduction of poly(diphenylene phthalide) (PDP) with metallic lithium in DMF at room temperature was studied by electronic and ESR spectroscopies. The main feature of the process is the presence of a long induction period (about 50 to 80 min) which is probably caused by the formation of small lithium particles and by adsorption of the polymer on the metal. At least four types of nonparamagnetic color centers characterized by overlapping absorption bands at 570, 660, 750, and 810 nm were detected in the reduced solution. The amounts of all types of the color centers in the solution show a complex dynamic behavior. Reduction of the polymer in the bulk of the solution is due to lithium colloid particles which give rise to a narrow asymmetric ESR singlet (g = 2.0023, ΔH = 0.03 mT, A/B ≈ 1.1–1.8) and absorb light in the region λ ～300–400 nm. Paramagnetic species with quartet ESR signal with a splitting of 0.1 mT and g = 2.0045 observed in the solutions being reduced at a polymer concentration of 0.2 mol L^?1 were attributed to radical anions of terminal anthraquinone groups (TAGs). The electron affinities of some molecules simulating the phthalide-containing unit of the polymer backbone, TAG, and a defect anthrone group were calculated in the B3LYP/6-311+G(d,p) approximation. For diphenylphthalide, the vertical electron affinity EA_vert = 0.21 eV, the adiabatic electron affinity EA_ad = 0.66 eV, the effective electron affinity EA_eff (with allowance for cleavage of C-O bond in the phthalide ring) = 1.23 eV. For anthrone group, one has EA_ad ～1.2 eV and for anthraquinone group, EA_ad ～2 eV. The electron affinities of the model compounds were also calculated with inclusion of the energy of solvation in two solvents (DMF and DMSO) and the energy of polarization in the PDP film. The electronic spectra of some compounds chosen as models for the expected products of reduction (anions and dianions) of the main phthalide-containing fragments in the polymer, TAGs, and defect anthrone groups were also calculated by the TD DFT B3LYP/6-311G(d,p) method. The presence of three types of chemical electron traps and the possibility of manifestation of strong absorption bands of these anions and dianions in the spectral region 500–900 nm precludes unambiguous selection and assignment of complex experimental electronic spectra observed in the course of PDP reduction. The possible role of TAGs in the electronic and photophysical processes in PDP is discussed.     

Mechanism of the Grignard reaction in terms of the cluster model of reaction center. A quantum-chemical study

Most probable paths of the classical Grignard reaction between ethyl bromide and Mg₃₁ cluster simulating the reaction center on the surface of metallic magnesium were analyzed in terms of the density functional theory [B3PW91/6-31G(d)]. Principal thermodynamic parameters of the radical reaction path, including the energy of adsorption of oxidant molecules on the cluster, the energy of formation of ethyl radicals, and the energy of their subsequent interaction with the surface, were calculated. The structure corresponding to the true transition state of the Grignard reaction was identified. The low energy of activation of the reaction occurring at the phase boundary (5.1 kcal/mol) indicated that the surface reaction of radical formation cannot be rate-determining.     

Oxidation of Zinc and Cadmium with Tricarbonylcyclopentadienylmolybdenum Chloride and Tricarbonylcyclopentadienyltungsten Chloride

The rate of the reaction of zinc and cadmium with tricarbonylcyclopentadienylmolybdenum chloride and tricarbonylcyclopentadienyltungsten chloride and the yield of the final products of these reactions were studied as influenced by the solvent nature. Kinetic features of oxidation of zinc and cadmium with tricarbonylcyclopentadienylmolybdenum chloride in the presence of dimethylformamide were determined. The thermodynamic parameters of adsorption of the oxidizing agent and the ligand on the metal surface were determined.     

Photodecomposition of chromium tricarbonyl complexes with styrene, stilbene, and 1,4-diphenylbuta-1,3-diene in solution

Photolytic decomposition of styrene, stilbene, and 1,4-diphenylbuta-1,3-diene tricarbonyl chromium complexes in solution results in elimination of the carbonyl ligands and formation of binuclear alkenylarene chromium complexes. The quantum yields and activation and kinetic parameters of these processes were determined, and a scheme was proposed to rationalize photoinitiated transformations of the organochromium compounds under study.     

Voltamperometric determination of uranium and plutonium in alkaline solutions

The simultaneous determination of U(VI), Pu(VI), Pu(V) in 0.5–4.0 M NaOH has been elaborated by means of classical and differential pulse voltamperometry. U(VI) is determined with a dropping mercury electrode (DME) at the half-wave potential of E_1/2=–0.89 V vs. Ag/AgCl reference electrode due to reduction to U(V). The limiting current or peak heights are proportional to uranium(VI) concentration in the range of 1.3.10^–7–3·10^–4 M U(VI). Deviation from proportionality is observed for higher concentrations due to polymerization of uranates. Pu(VI) and Pu(V) are determined with a platinum rotating electrode at E_1/2=–0.02 V due to the reaction Pu(VI)+e^–»Pu(V) and with DME at E_1/2=–1.1 V due to the reduction to Pu(III). The limiting currents of both Pu(VI) and Pu(V) are proportional to their concentrations in the range of 4·10^–6–1.2·10^–3 M Pu. The determination of U(VI), Pu(VI), Pu(V) is not interfered by the presence of the following salts: 2M NaNO₃, 2M NaNO₂, 1.5M NaAlO₂, 0.5M NaF and ions of Mo(VI), W(VI), V(V), Cu(II). The presence of CrO ₄ ^2– and FeO ₂ ^– ions disturbs the determination of U(VI) in 1–4M NaOH, however, contribution of the reaction Fe(III)+e^–»Fe(II) to uranium reduction peak can be calculated from the height of the second peak Fe(II)+2 e^–»Fe(0).     

Synthesis of Polynuclear Organometallic and o-Quinone Compounds by Direct Metal Oxidation in Nonaqueos Solutions

A review of papers concerned with the synthesis of polynuclear organometallic compounds by direct metal oxidation with organoelemental halides is presented. The effect of solvent nature on the rate of metal oxidation in nonaqueous solutions is considered. The mechanism of metal oxidation with o-quinone in aprotic dipolar solvents is suggested.