Homolytic dissociation of the carbon-element σ bonds by Grignard reagents

The reaction of 2-ethyl-3-tetrahydrofuryl thiocyanate (I) and triphenylacetonitrile (VIII) with methylmagnesium iodide in ether was studied using GC/MS, PMR and¹³C NMR spectroscopy. The reaction of (I) with CH₃MgI gives the product of the homolysis of the C-S bond, namely, bis(2-ethyl-3-tetrahydrofuryl) disulfide (II), in 81% yield. This reaction is assumed to be general in nature since triphenylacetonitrile (VIII) is also homolytically cleaved by the action of CH₃MgI to give triphenylmethane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2886–2888, December, 1991.     

A study of the tautomerism of the N-alkyl-3-methoxycarbonyl-4-piperidinones and their hydrochlorides

The positions of the equilibria of N-alkyl-3-methoxycarbonyl-4-piperidinones in the liquid state, in water, in alcohols, and in CCl₄ have been determined by IR and UV spectroscopy. It has been shown that Meyer's equation is not satisfied for them. This is due to the high steric requirements of the solvating electron pair of the nitrogen atom. On the basis of the fact that on passing from the methyl ester of cyclohexan-1-one-2-carboxylic acid to the N-alkyl-3-methoxycarbonyl-4-piperidones the position of the equilibrium in the liquid state and in CCl₄ does not shift in the direction of the enol it is deduced that the spatial requirements of the free electron pair of the nitrogen atom do not appreciably exceed the steric requirements of the hydrogen atom. The IR and UV spectra of the chlorides of the N-alkyl-3-methoxycarbonyl-4-piperidinones in the solid state and in water and in alcohols are given.     

Effective excitation cross section and lifetime of Er<Superscript>3+</Superscript> ions in Si: Er light-emitting diodes fabricated by sublimation molecular-beam epitaxy

A series of Si: Er electroluminescent diode structures is fabricated by sublimation molecular-beam epitaxy. The diode structures efficiently emit at a wavelength of 1.5 μm under conditions of p-n junction breakdown at room temperature. The effective cross section of excitation of Er³⁺ ions with hot carriers heated by the electric field of a reverse-biased p-n junction and the lifetime of Er³⁺ ions in the first excited state ⁴I_13/2 are determined for structures that emit in a mixed breakdown mode and are characterized by the maximum intensity and excitation efficiency of the Er³⁺ electroluminescence.     

Spin polarization of the current in a correlated one-dimensional conductor with an impurity

The spin transport as the current flows through an impurity in a one-dimensional conductor is analyzed. The interacting electrons are described in terms of the Luttinger liquid theory. Both the Coulomb and short-range interactions are considered; the latter appears when the gate screens the long-range part of the Coulomb potential. The cases of magnetic and nonmagnetic impurities are considered. It has been revealed that, for a magnetic impurity, the electric current flow induces the generation of the spin current, which has direct and alternating components. At low temperatures and voltages, the current can be completely spin-polarized. For a nonmagnetic impurity, the spin current generation is absent. The spin current flowing though the wire affects the current-voltage characteristic for both magnetic and nonmagnetic impurities. The results have been obtained for a rather strong electron-electron interaction.     

Effect of treatment in supercritical CO<Subscript>2</Subscript> on the composition and structure of tealeaf and cellulose

The influence of the pretreatment procedures with supercritical CO₂ (SC-CO₂) on the elemental composition of tealeaf is studied. Fourier-transform infrared absorption spectroscopy is used to examine the effect of SC-CO₂ on the structure of Chinese green tea and cellulose.     

Chernoff approximations of Feller semigroups in Riemannian manifolds

Chernoff approximations of Feller semigroups and the associated diffusion processes in Riemannian manifolds are studied. The manifolds are assumed to be of bounded geometry, thus including all compact manifolds and also a wide range of non-compact manifolds. Sufficient conditions are established for a class of second order elliptic operators to generate a Feller semigroup on a (generally non-compact) manifold of bounded geometry. A construction of Chernoff approximations is presented for these Feller semigroups in terms of shift operators. This provides approximations of solutions to initial value problems for parabolic equations with variable coefficients on the manifold. It also yields weak convergence of a sequence of random walks on the manifolds to the diffusion processes associated with the elliptic generator. For parallelizable manifolds this result is applied in particular to the representation of Brownian motion on the manifolds as limits of the corresponding random walks.     

Waves on the He-II Surface,Excited by a Heat Flux in the Bulk

Journal of Experimental and Theoretical Physics - The conditions for the occurrence of an instability generated on the free surface of superfluid He-II by a constant or variable heat flux Q in the...     

Infrared E-type band profiles of acetonitrile in condensed media: orientational diffusion and free rotation

Infrared spectra of liquid acetonitrile (CH3CN) and its solutions in CCl4, CS2, chloroform, dichloromethane, benzene-d6, acetone-d6 and dimethyl sulfoxide-d6 have been studied. E-type bands under investigation (v5 = 3009, v6 = 1448 and v7 = 1041 cm(-1)) were reproduced by the sum of two Cauchy-Gauss components, the narrower (n) and the broader (b) ones. The different temperature behaviour of the components has been found: the integrated intensities of the narrower components, In, decrease with the temperature, while the intensities of the broader ones, Ib, increase. The narrower components of the bands were explained within the framework of the orientational diffusion mechanism. The broader components of v6 and v7 were attributed to the unresolved gas-like vibration-rotational absorption of the molecules. The enthalpy difference between the molecules absorbing via these two different mechanisms was determined from the dependence of ln(In/Ib) upon T(-1) :deltaH0 = 1.26+/-0.15 kcal mol(-1). The broader component of v5 is assumed to be mainly due to interactions of C-H stretching vibrations with single particle and collective motions of molecular dipoles. The narrower components' widths were used for evaluating the spinning diffusion constant of CH3CN. The absorption in C-H stretching region was found to be strongly affected by solvent. These effects were explained within the framework of hydrogen bond formation between the CH3-group of acetonitrile and H-bond acceptor groups of the solvent molecules.