Tautomeric properties and gas-phase structure of 3-chloro-2,4-pentanedione

The tautomeric properties of alpha-chlorinated acetylacetone, 3-chloro-2,4-pentanedione CH3C(O)-CHCl-C(O)CH3, have been investigated by gas electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximations with different basis sets up to cc-pVTZ). Analysis of the GED intensities resulted in the presence of 100(2)% enol tautomer at 269(8) K. The following skeletal geometric parameters (rh1 values) of the molecule, which possesses Cs symmetry, were derived: r(C=C) = 1.378(3) A, r(C-C) = 1.450(3) A, r(C=O) = 1.243(3) A, r(C-O) = 1.319(3) A, r(O-H) = 1.001(4) A, r(C-Cl) = 1.752(4) A, angleC-C=C = 121.3(1.0) degrees , angleC=C-O = 119.9(1.2) degrees , angleC-C=O = 119.1(1.2) degrees . Due to very small contributions of the keto tautomer in alpha-chlorinated acetylacetone and its parent species, the effect of alpha-chlorination on tautomeric properties cannot be derived from experimental data. Quantum chemical calculations (B3LYP/6-31G**, B3LYP/cc-pVTZ, and MP2/cc-pVTZ) predict that alpha-chlorination of acetylacetone has no pronounced effect on the tautomeric properties. On the other hand, similar calculations for 1-chloro-1,3-butanedion, ClC(O)-CH2-C(O)CH3, demonstrate that chlorination in one beta position destabilizes the enol tautomer. In both chlorinated species the enol form is strongly preferred.     

Maghemite nanocrystal impregnation by hydrophobic surface modification of mesoporous silica

Here, we report the design of a hybrid inorganic/organic mesoporous material through simultaneous pore engineering and hydrophobic surface modification of the intramesochannels to improve the uptake of superparamagnetic maghemite nanocrystals via impregnation techniques. The mesoporous material of the SBA-15 type was functionalized in situ with thiol organo-siloxane groups. Restricting the addition of the thiol organo-siloxane to 2 mol % yielded an inorganic/organic hybrid material characterized by large pores and a well-ordered hexagonal p6mm mesophase. The hydrophobic surface modification promoted the incorporation of 7.5 nm maghemite (gamma-Fe2O3) nanocrystals, prepared through temperature-controlled decomposition of iron pentacarbonyl in organic solvents. The hydrophobic, oleic acid capped superparamagnetic maghemite nanocrystals were incorporated into the porous network via wet impregnation from organic suspensions. Combining diffraction, microscopy, and adsorption data confirmed the uptake of the nanocrystals within the intramesochannels of the silica host. Magnetization dependencies on magnetic field at different temperatures show a constriction in the loop around the origin, which indicates immobilization of maghemite nanocrystals inside the thiol-functionalized silica host.     

Structure and Energetics of β-Diketonates. XII. Structure of Lanthanide tris-Dipivaloylmethanates for Er(thd)3 Used as an Example

A simultaneous electron diffraction and mass spectroscopic study of saturated vapors of erbium tris-dipivalylmethanate has revealed that at 136(5)°C, the vapor consists solely of Er(thd)₃ molecules. Electron diffraction data may be described by two alternative models (of C_3 and D_3 symmetry), for which r_a, r_g, and r structural parameters have been determined. D₃ symmetry is recognized to be preferable for free Er(thd)₃ molecules. The main structural parameters of the model are r (Er – O) 2.218(5), r (O – C) 1.279(5), r (C – C_r) 1.404(6), r (C – C_t) 1.512(3), r(C_t – C_m) 1.542(5), r (rm C_m– H) 1.804(4) , The ErO 75.0(0.4)°. The ErO₆ coordination polyhedron has a structure close to an antiprism. A rotational angle of the O–O–O trigonal face relative to the position in a regular prism is 20.7(0.8)°. Possible reasons for the differences in the structure of Er(thd)₃ molecules in the gas phase and crystal are discussed.     

Coupling between global geometry and the local hall effect leading to reconnection-layer symmetry breaking

The coupling between the global reconnection geometry and the local microphysics, caused by the Hall effect, is studied during counterhelicity plasma merging in the magnetic reconnection experiment. The structure of the reconnection layer is significantly modified by reversing the sign of the toroidal fields, which affects the manifestation of the Hall effect in the collisionless regime. The local two-fluids physics changes the global boundary conditions, and this combination effect consequently provides different reconnection rates, magnetic field structure, and plasma flow patterns for two different counterhelicity merging cases in the collisionless regime.     

Influence of External Conditions on the Relation between the Physical and Chemical Processes in the Thermodegradation of Plasticized Poly(Vinyl Chloride)

The heat-induced loss of plasticizer from and dehydrochlorination of poly(vinyl chloride) plasticized with dioctyl phthalate is studied by thermogravimetric analysis, IR spectroscopy, and colorimetry. Specific features and general regularities of the processes at high (200–320°C) and medium (100–132°C) temperatures are established. It is shown that the dehydrochlorination and oxidation processes dominate in confined space whereas, in unconfined space, plasticizer is lost largely through evaporation. The activation energies of the initial stages of the processes are determined.     

Complexes of Lanthanide (Dy,Er, Yb) Thiocyanates with Tetramethylphenanthroline. Synthesis,Thermolysis, and SMM Properties

Russian Journal of Coordination Chemistry - The mononuclear neutral complexes [Ln(Me4Phen)2(H2O)(NCS)3]·Me4Phen·0.75EtOH (Ln = Dy, Er, Yb) were prepared for the first time by the reaction...     

Spectroelectrochemical Properties and Catalytic Activity in Cyclohexane Oxidation of the Hybrid Zr/Hf-Phthalocyaninate-Capped Nickel(II) and Iron(II) tris-Pyridineoximates and Their Precursors

The in situ spectroelectrochemical cyclic voltammetric studies of the antimony-monocapped nickel(II) and iron(II) tris-pyridineoximates with a labile triethylantimony cross-linking group and Zr(IV)/Hf(IV) phthalocyaninate complexes were performed in order to understand the nature of the redox events in the molecules of heterodinuclear zirconium(IV) and hafnium(IV) phthalocyaninate-capped derivatives. Electronic structures of their 1e-oxidized and 1e-electron-reduced forms were experimentally studied by electron paramagnetic resonance (EPR) spectroscopy and UV−vis−near-IR spectroelectrochemical experiments and supported by density functional theory (DFT) calculations. The investigated hybrid molecular systems that combine a transition metal (pseudo)clathrochelate and a Zr/Hf-phthalocyaninate moiety exhibit quite rich redox activity both in the cathodic and in the anodic region. These binuclear compounds and their precursors were tested as potential catalysts in oxidation reactions of cyclohexane and the results are discussed.     

Effect of phosphate doping on electric properties and chemical stability of Ba<Subscript>4</Subscript>Ca<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>11</Subscript> protonic conductor

Conductivity of perovskite phosphate–substituted solid solutions of Ba₄Ca₂Nb_{2 –x} P _x O₁₁ (0.0 ≤ x ≤ 0.5) was studied as a function of temperature, partial pressure of oxygen and water vapors. It is proved that the studied systems are protonic conductors at the temperatures below 600°C in the atmosphere with elevated content of water vapors (pH₂O = 1.92 × 10^–2 atm). Introduction of the tetrahedral [PO₄] group in the complex oxide matrix of Ba₄Ca₂Nb₂O₁₁ results in an increase in the oxygen–ionic (dry air, pH₂O = 1.91 × 10^–4 atm) and protonic conductivities (wet air, pH₂O = 1.92 × 10^–2 atm). Is it found that the doping causes a considerable increase in chemical stability of phases with respect to carbon dioxide.     

Simplified Navier-Stokes equations for computing viscous gas flow past long bodies

Simplified Navier-Stokes equations are applied to analyze the flow of supersonic viscous gas at moderately large Reynolds numbers near the lateral surface of long bodies. Numerical integration of the equations is performed by the marching method, stabilizing in each step the solution of the nonstationary system of equations in the longitudinal coordinates. We consider the flow past cylinders and cones with a spherical blunt nose. We investigate the effect of the Reynolds number and the body shape on the flow field, the drag coefficient, and the heat flux. The numerical solutions of simplified and complete Navier-Stokes equations are compared.Translated from Vychislitel'naya Matematika i Matematicheskoe Obespechenie EVM, pp. 231–239, 1985.