Reactions of dichlorocarbene,dichlorosilylene, and dichlorogermylene with carboranes(12). A theoretical study

Insertion of CCl₂, SiCl₂, and GeCl₂ into the B-H and C-H bonds of the carborane(12) molecules as well as into the B-Hal, C-Hal bonds of some halogen-substituted ortho-carboranes are studied at the B3LYP/6-311+G(d,p) and M06-2X/6-311+G(d,p) levels of theory. Thermodynamic parameters of the reactions are calculated and their variation for the isomeric carboranes(12) and for a series of carbenoid species is shown. For several insertion reactions the energies of activation are calculated based on the model of three-center synchronous transition state. The energy barriers are regularly varied depending on the position of the B-H bond in the carborane molecule.     

A Diffusion-Kinetic Model for Radiation-Chemical Transformations of Oxalic Acid and Oxalate Ions in Aqueous Solutions

A diffusion-kinetic model for the radiation-chemical degradation of oxalic acid and oxalates in aqueous solutions was developed. The model adequately describes published data on the formation of H₂, H₂O₂, and CO₂ over wide ranges of acid concentrations and pH values.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 4, 2005, pp. 250–254.Original Russian Text Copyright © 2005 by Gordeev, Ershov, Kosareva.     

Temperature dependence of the quadruple interaction and the diffusion of muonium atoms in α-quartz

The results of an experimental investigation of the quadrupole interaction of muonium atom in-quartz in the temperature region 75–300 K are presented. It is show that the observed temperature dependence of the quadrupole interaction parameters is fully determined by the diffusion of muonium.     

HF-plasmatron experiment and numerical simulation of heat transfer in underexpanded dissociated-nitrogen jets

Experiments on heat transfer in underexpanded supersonic jets of high-enthalpy nitrogen are performed on the VGU-4 induction high-frequency plasmatron at a pressure of 10.4 GPa in a compression chamber. At gas flow rates of 2.4 and 3.6 g/s and HF generator powers of 45 and 64 kW the heat fluxes to the copper, stainless steel, MPG-7 graphite, and quartz surfaces are measured at the stagnation point of a water-cooled cylindrical, flat-ended model, 20 mm in diameter. In the same regimes the stagnation pressures are measured. The effect of the surface catalyticity with respect to nitrogen atom recombination on the heat flux is demonstrated and the qualitative catalyticity scale of the studied materials is established. In the supersonic regimes nonequilibrium nitrogen plasma flow in the discharge channel of the plasmatron and the underexpanded jet flow past the model are numerically simulated for the experimental conditions. The experimental and calculated data on the stagnation pressures and the heat fluxes to cooled surfaces of the metals, graphite, and quartz are compared.     

Electrochemical intercalation of lithium into diamond-pyrocarbon nanocomposites

Physics of the Solid State - The electrochemical behavior of composite materials based on nanodiamond and carbal is investigated in the course of cathodic intercalation of lithium from an LiPF6...     

First‐principles X‐ray absorption dose calculation for time‐dependent mass and optical density

A dose integral of time‐dependent X‐ray absorption under conditions of variable photon energy and changing sample mass is derived from first principles starting with the Beer–Lambert (BL) absorption model. For a given photon energy the BL dose integral D(e, t) reduces to the product of an effective time integral T(t) and a dose rate R(e). Two approximations of the time‐dependent optical density, i.e. exponential A(t) = c + aexp(?bt) for first‐order kinetics and hyperbolic A(t) = c + a/(b + t) for second‐order kinetics, were considered for BL dose evaluation. For both models three methods of evaluating the effective time integral are considered: analytical integration, approximation by a function, and calculation of the asymptotic behaviour at large times. Data for poly(methyl methacrylate) and perfluorosulfonic acid polymers measured by scanning transmission soft X‐ray microscopy were used to test the BL dose calculation. It was found that a previous method to calculate time‐dependent dose underestimates the dose in mass loss situations, depending on the applied exposure time. All these methods here show that the BL dose is proportional to the exposure time D(e, t) ? K(e)t.     

Pyrroloindoles. 8. Electrophilic substitution in the 1H,5H-pyrrolo[2,3-f]indole and 3H,6H-pyrrolo[3,2-e]indole series

The principles of the electron density distribution in 1H,5H-pyrrolo [2,3-f]indole and 3H,6H-pyrrolo[3,2-e]indole molecules were determined on the basis of quantumchemical calculations. These results were confirmed by the results of the investigated electrophilic-substitution reactions. The reaction centers of these compounds proved to be the same positions as in indole, viz., the 3 and 7 and 1 and 8 positions, respectively. The impossibility of 1,8-disubstitution in the angular heteroring was demonstrated in the case of bulky substituents; this was explained by a steric effect.See [1] for communication 7.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1086–1091, August, 1983.     

Formation of pyrimidin-4-one derivatives in the reaction of 6-aryl-2,2-dimethyl-1,3-dioxin-4-ones with ketene aminals

N. D. Zelenskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1225–1226, May, 1992.