Electrochemical reduction of 1,1-dihalo-2,2-disubstituted cyclopropanes

The electrochemical reduction of 1,1-dihalo-2-R-2-methylcyclopropanes was studied by polarography and preparative electrolysis. A mixture of stereoisomeric monoboro- and monochlorocyclopropanes was obtained with preparative yield of 60–70% in preparative electroreduction in methanol against a background of 0.1 M LiClO₄. In the case of bromine derivatives of cyclopropanes (except when R = CN) an effect was found on the part of the current density on the ratio of cis and trans isomers, which was interpreted as a change, in dependence on current density, of the contributions of the reactions of reduction of the starting compounds (S_N2 mechanism) and ionic pairs (S_N1 mechanism). The effect of the solvent (CHCl₃, DMF, DMSO, MeOH) and background salt (LiClO₄, Et₄NBr) on the ratio of stereoisomers is in agreement with this interpretation.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Science Center, Russian Academy of Sciences, Kazan. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 2023–2032, September, 1992.     

Proximity effect in superconductor/ferromagnet layered system: Influence of superconductivity on magnetic properties of Nb/Fe epitaxial bilayers

Magnetic and superconducting properties of Fe/Nb epitaxial bilayers have been studied. Single crystal Fe/Nb (110) bilayers with a Nb thicknessd _Nb in the range from 250 to 650 Å and with a Fe thicknessd _Fe in the range from 7 to 27 Å were prepared using molecular beam epitaxy techniques. Magnetization measurements showed the existence of a magnetically “dead” Fe-interface layer with a thicknessd _NM varying strongly with minor modifications of the growth conditions. For bilayers with a small magnetic layer thicknessd _M and a smalld _NM the FMR measurements revealed an anomalous decrease of the effective magnetization 4πM _eff of the ferromagnetic Fe layer below the superconducting transition temperatureT _c. The absolute change of 4πM _eff belowT _c depends strongly on the actual values ofd _M andd _NM: upon decreasing bothd _M andd _NM the effect increases considerably. As a possible mechanism for the anomalous temperature dependence of 4πM _eff belowT _c we discuss a spatial modulation of ferromagnetic order due to a modification of the RKKY inter-action in the superconducting state.     

Experimental investigation of the role of the triplet pairing in the superconducting spin-valve effect

An important role of the morphology of a superconducting layer in the superconducting spin-valve effect has been established. The triplet pairing induced by the superconductor/ferromagnet proximity effect has been experimentally investigated for samples CoO_x/Py1/Cu/Py2/Cu/Pb (where Py = Ni_0.81Fe_0.19) with a smooth superconducting layer. The optimization of the parameters of this structure has demonstrated a complete switching between the normal and superconducting states with a change in the relative orientation of magnetizations of the ferromagnetic layers from the antiparallel to orthogonal orientation. A pure triplet contribution has been observed for the sample with a permalloy layer thickness at which the superconducting spin-valve effect vanishes. A direct comparison of the experimental data with the theoretical calculation of the temperature of the transition to the superconducting state has been performed for the first time.     

Synthetic glycosides containing two isosteviol fragments functionalized with D-glucopyranose

The synthesis of isosteviol (16-oxo-ent-beyeran-19-oic acid) glycosides in which two isosteviol fragments functionalized with tetra-O-acetyl-D-glucopyranose are linked through a diester spacer is described for the first time.     

Structure of interfaces in thin-film metallic multilayer heterostructures

It is demonstrated that the structure of interfaces in thin-film metallic multilayers can be predicted from the phase diagrams of binary alloys of metals constituting the multilayers. Experimental data on the small-angle X-ray reflectivity and magnetization of the samples are used for characterizing the structure of the interfaces.     

Experimental observation of the spin screening effect in superconductor/ferromagnet thin film heterostructures

When studying the nuclear magnetic resonance (NMR) of ⁵¹V nuclei in superconductor/ferromagnet thin film heterostructures, anomalous behavior of the NMR signal was observed. This effect was manifested as a systematic distortion of the high-field wing of the resonance line. We consider this to be the first experimental evidence for penetration of ferromagnetism into a superconductor.     

Electrochemical carbonylation of 2,2-dibromo-1-carbomethoxy-l-methylcyclopropane

Direct and indirect electrochemical reductive carbonylation of 2,2-dibromo 1-carbomethoxy-l-methylcyclopropane involving Ni^II ions and CO was studied in an McCN-benzene (3 : 1) mixture in the presence of n-PrOH and Et₂NH. 2-Bromo 1-carbomethoxy-l-methylcyclopropane with cis-configuration of substituents is formed upon-direct carbonylation in the case of n-propanol, while ester or amide of I-carbomethoxy 1-methylcyclopropanecarboxylic acid are obtained in the other cases. In the presence of amine, the direct electrochemical carbonylation occurs under milder conditions and results in a different ratio of stereoisomeric products.Translated fromIzvestiya Akademii Sauk. Seriya Khimicheskaya, No. 3, pp. 659–662, March, 1996.     

Thermal instability of a horizontal layer of viscoelastic liquid

The convective instability of a horizontal layer of viscoelastic liquid during heating from below has been examined. Critical values of the Rayleigh numbers for two forms of limiting conditions have been determined.S. M. Kirov Kazansk Chemicotechnological Institute. Translated from Mekhanika Polimerov, No. 2, pp. 331–335, March–April, 1976.     

Kinetics of the mediatory reduction ofgem-dichlorocyclopropanes

The effect of the nature of organic electron transfer agents and of Pt^II, Pd^II, Rh^II, Co^II, Ni^II, Cu^II, Cr^III, Mn^II, Ti^III, V^III, Zn^II, and Ag^I metal ions on the kinetics of the homogeneous reduction ofgem-dichlorocyclopropanes has been studied. Pt^II, Pd^II, Rh^III, Co^II, and Ni^II ions accelerate this process, V^III and Ag^I ions exert practically no effect on the reduction rate, and the rest of the metal ions exhibit inhibitor properties.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1407–1410, August, 1993.