Analysis of influence of spin relaxation on form of nuclear magnetic resonance spectra in liquids with radiofrequency pumping

For a model system of two nonequivalent nuclei with spin 1/2, the NMR spectrum of one of the nuclei has been calculated under conditions of pumping of the second spin, and a study has been made of the spectral transformation upon changing the times of transverse and longitudinal relaxation of both spins. It has been established that the form of the spectrum undergoes qualitative changes. An increase in the rate of transverse relaxation not only broadens the observed lines, but simultaneously changes the character of motion of the spins in the pumping field: With increasing relaxation rate, the motion is converted from coherent motion (nutation) to incoherent motion (transitions between levels, saturation effect). Transformations of the spectrum are related specifically to these changes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 4, pp. 436–443, July–August 1987.     

Photochlorination of tetramethylsilane and hexamethyldisilane in the gas phase

Preliminary studies of the reaction of chlorine with tetramethylsilane and hexamethyldisilane in the gas phase show that the photochlorination of tetramethylsilane is complex, giving different products from the corresponding reaction in solution and having an explosion boundary. At pressures below the explosion boundary the main products are ethylene, hydrogen chloride, dimethylchlorosilane, and more highly chlorinated methylsilanes. Above the explosion boundary main products after explosion are methane, acetylene, ethylene, hydrogen chloride, and silicon tetrachloride. Hexamethyldisilane reacts rapidly with chlorine in the dark, as it does in solution, forming mainly trimethylchlorosilane along with similar products to those found with tetramethylsilane. Subsequent photochlorination of trimethylchlorosilane follows a similar course to that of tetramethylsilane in the gas phase. Tentative mechanisms involving “hot” molecules are suggested.     

Reaction of esters of thio acids of trivalent arsenic with organomagnesium compounds

Conclusions Depending on the molar ratios, the esters of the thio acids of trivalent aresnic are alkylated by organomagnesium compounds to give the corresponding tertiary arsines or the esters of the thio acids of trivalent arsenic.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 963–965, April, 1972.     

Methane conversion with carbon dioxide on nickel aluminides

The catalytic activity of several samples based on nickel aluminides in methane conversion with carbon dioxide was studied. Nickel aluminides were prepared by the method of self-propagating high-temperature synthesis. The Ni₃Al system containing the nickel metal phase exhibited high activity at temperatures above 1073 K. The systems based on Ni₂Al₃ and NiAl only containing intermetallic compound phases were inactive.     

Synthesis of 4-Formyl-3-cyclopentene-1,1,2-tricarbonitriles

β,β,γ,γ-Tetracyanoalkanones react with acrolein at a high rate to afford the corresponding 2-substituted 4-formyl-3-cyclopentene-1,1,2-tricarbonitriles in high yields. The reaction occurs under mild conditions and is quite applicable for modification of natural and biologically active compounds possessing an R′CHC(O)CR₃ fragment to obtain their derivatives containing three cyano groups.     

Analytical Azo Coupling Reactions: A Quantum-Chemical Consideration

Azo coupling reactions of 1-aminonaphthalene with naphthalene-1-diazonium and 4-sulfobenzene-diazonium cations are studied by quantum chemistry. It is found that the reactions are orbital controlled and their regioselectivity is unambiguously governed by the thermodynamic properties of the intermediate σ-complexes and by the effect of the aqueous medium. The latter causes high site selectivity, providing the choice of one of the two possible reaction channels predicted on the basis of quantum-chemical calculations of the isolated molecular systems. As a result, azo coupling occurs at the 4-position of the 1-aminonaphthalene molecule. Additionally, the aqueous medium provides the selection of analytical forms, namely, the protonated azo coupling products that have the quinone-hydrazone structure. On the basis of the quantum-chemical study, the analytical performances of the two azo coupling reactions mentioned above are discussed.     

Cyclocondensation of [1-Cyano-2-(methylsulfanyl)vinyl]triphenylphosphonium Iodide with Amidine Nucleophiles

The substituted vinylphosphonium salt (E)-MeSCH=C(CN)P⁺Ph₃I⁻ readily cyclizes under the action of benzamidine and 3-amino-s-triazole, but it does not enter cyclocondensation with 2-aminopyridine. The structure of the cyclization product with 3-amino-s-triazole was confirmed by its transformation to 7-imino-6-(triphenylphosphoranylidene)-6,7-dihydro-s-triazolo[1,5]pyrimidine which was identified by X-ray diffraction. This stabilized ylide and its analogs proved useful starting materials for regioselective syntheses of 2-R-4-alkyl-4,7-dihydro-s-triazolo[1,5-a]pyrimidin-7-ones.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 4, 2005, pp. 565–570.Original Russian Text Copyright © 2005 by Smolii, Muzychka, Chernega, Drach.     

Electron impact mass spectral interpretation for some thiophosphoryl-p-acetylaminobenzenesulfonamides

This work discusses the synthesis and the fragmentation patterns for 2-(p-acetylaminosulfonamido)-2-thiono-(5,5-dimethyl-1,3,2-dioxaphosphorinane)(1) and for the p-acetylaminosulfonylamides of O,O-diethylthiophosphoric acid (2), O,O-diphenylthiophosphoric acid (3), dimethylaminocyclohexylthiophosphoric acid (4), and diethylaminophenylthiophosphoric acid (5). A thionamidic-thiolimidic structure was attributed to compounds 1-5, consistent with their IR and NMR spectra. EI mass spectra at 70 eV, high resolution (HR) mass measurements and metastable ion spectra were used to elucidate the fragmentation processes and to determine the kinetic energy release values associated with the metastable ion dissociations. HR accurate mass measurements were used to confirm the compositions of the more abundant ions.     

Spectrophotometric determination of bismuth after extraction of hexadecyltributylphosphonium tetraiodobismuthate(III) by microcrystalline benzophenone

Bismuth (0–110 μg) is determined spectrophotometrically at 495 nm after its adsorptive extraction from dilute sulphuric acid as hexadecyltributylphosphonium tetraiodobismuthate(III) on microcystalline benzophenone and dissolution of the solid phase in carbon tetrachloride. The effects of acidity, diverse ions and masking studies are reported. The system is applied to the determination of bismuth in pharmaceutical samples.