Rate of14N2 desorption from the surfaces of nitrides in the presence and absence of15N2 in the gas phase

The rates of¹⁴N₂ desorption from the surfaces of nitrides have been measured in the presence and absence of¹⁵N₂ in the gas phase. Whatever the adsorption heat and the form of surface species, the adsorption of¹⁵N₂ molecules does not affect the rate of¹⁴N₂ desorption.

---

¹⁴N₂ ¹⁵N₂ . , ¹⁵N₂ ¹⁴N₂.

     

The first three aromatic tribromides of the [2.2]paracyclophane series

From the reaction mixtures in the uncatalyzed polybromination of [2.2]paracyclophane by the action of excess Br₂ in CCl₄, there have been found along with the known products — 4,15- and 4,16-dibromo[2.2]paracyclophanes — two new aromatic tribromides of this series, which have been isolated in pure form: 4,12,15- and 4,15,16-tribromo[2.2]paracyclophanes. Special experiments demonstrated that the mixtures of these tribromides are formed as a result of competitive monobromination of 4,15-dibromo[2.2]paracyclophane; the 4,15,16-tribromo[2.2]paracyclophane, together with still another newly isolated isomer of this series — 4,8,12-tribromo[2.2]paracyclophane — is formed as a result of competitive monobromination of 4,16-dibromo[2.2]paracyclophane. As an explanation of the features of the orienting effect of substituents in these competing reactions, a rule was proposed: On the conventional orientation (from the electronic point of view) of entry of the bromine atom into the substituted ring (para > ortho > meta), a steric limitation is imposed on its attack in the pseudo-gem-position, owing to the bulky bromine atom that is transannularly positioned above it in the neighboring aromatic ring. The structures of all of the tribromides were established on the basis of elemental analyses, mass spectrometry, and¹H NMR spectrometry (including PMR using the homonuclear Overhauser effect). The data obtained in this work indicate that the 4,12,15-tribromo[2.2]paracyclophane and 4,15,16-tribromo[2.2]paracyclophane are predecessors of the two tetrabromides previously obtained by Cram — 4,7,12,15- and 4,5,15,16-tetrabromo[2.2]paracyclophanes; and the 4,8,12-tribromo[2.2]paracyclophane is a possible predecessor of 4,8,12,16-tetrabromo[2.2]paracyclophane, which is unknown up to the present time.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1837–1843, August, 1992.     

Electrodeposition of Cu-Sn Alloy from Oxalic Acid Electrolyte in the Presence of Amine-containing Surfactants

Russian Journal of Applied Chemistry - Method of potentiodynamic polarization was used to study the electrodeposition of a copper-tin alloy from an oxalic acid electrolyte with addition of...     

Stimulated Raman Scattering in Metal-Dielectric Nanocomposites with Spectrally Degenerate Dielectric Constant

JETP Letters - The effects of enhancement of stimulated Raman scattering in titanium oxynitride (TiON) nanofilms are considered. The mechanism of giant amplification of a Stokes wave is based on,...     

Applying reactive ionic-beam etching to correcting the shape of X-ray mirrors

A procedure for correcting the shape of cylindrical surfaces by means of reactive ionic-beam etching is presented. The results from an experiment on manufacturing a glass surface as an elliptical cylinder are shown.     

Ethylene Hydrogenation on a Platinum Nanocoating at Various Electric Potentials

The possibility of controlling the rate of ethylene hydrogenation on a platinum nanocoating is established by applying to it electric potentials of different polarities and magnitudes from an external voltage source. At a negative potential of ?10 V, the hydrogenation rate increases by 4%, whereas at a positive potential of +10 V, the hydrogenation rate increases by 42% under the conditions of the experiment at room temperature, atmospheric pressure, and an initial mixture composition of 0.09C₂H₄ + 0.91H₂. Quantum-chemical calculations of the energy of the reaction of platinum hydride with hydrogen, Pt₂H₂ + H₂ → Pt₂H₃ + H, and the energy characteristics of similar reactions involving negatively and positively charged Pt₂H₂ are performed. It has been demonstrated that the presence of a negative or positive charge on Pt₂H₂ lowers the endothermicity of formation of H radicals by 18.4 or 22.5 kcal/mol, respectively. Based on the calculation results, a mechanism is proposed to explain the effect of the charge of a platinum coating on its catalytic activity in ethylene hydrogenation.     

Synthetic transformations of higher terpenoids. XXI.* Preparation of phlomisoic acid and its <Emphasis Type="Italic">N</Emphasis>-containing derivatives

A method for preparing 15,16-epoxylabda-8(9),13(16),14-trien-18-oic (phlomisoic) acid was proposed. Its structure was confirmed by an XSA. N-containing derivatives of phlomisoic acid that contained amines, hydrazides, and methyl esters of amino acids on the C-18 atom in addition to (2-oxo-2-aminoacetyl)-substituted derivatives of the C-16 methyl ester of phlomisoic acid were prepared.     

Electrocatalytic intercalator-induced winding of double-stranded DNA with polyaniline

The intercalation of doxorubicin into double-stranded DNA stimulates the electocatalyzed oxidation of aniline to polyaniline and its winding on the DNA template.     

Complex-forming and selectivity properties of substituted tetraphenylethylenediphosphine dioxides with respect to alkali metal cations

The complex-forming reactivity of mono- and disubstituted ethylenediphosphine dioxides of the general formula Ph₂P(O)CH₂C(R¹R²)P(O)Ph₂, and of a tetraphosphorylated monopodand, ortho-bis[4,5-bis(diphenylphosphinyl)-pentoxy]benzene, relative to alkali metal cations have been determined conductometrically in THF-CHCl₃ medium (4:1). Introduction of alkyl substituants in the ethylene bridge of tetraphenylethylenediphosphine dioxide increases its Li/Na selectivity; maximum Li/Na selectivity equal to 40 is observed for the dimethyl-substituted tetraphenylethylenediphosphine dioxide derivative. Among the ligands examined herein the hexadentate tetraphosphoryl-containing monopodand ortho-bis[4,5-bis(diphenylphosphinyl)pentoxy]benzene was found to be the most effective complex-forming agent with respect to lithium (log=6.0), with a high Li/Na selectivity value equal to 40. The syntheses of 1,1-dimethyltetraphenylethylenediphosphine dioxide and of ortho-bis[4,5-bis(diphenylphosphinyl)pentoxy]benzene are described.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 873–877, April, 1990.The authors wish to thank Z. N. Vostroknutovii for carrying out the stability constant measurements in anhydrous acetonitrile.