Topological incremental scheme for calculating13C NMR chemical shifts in polysubstituted benzenes with substituents of one kind

A new topological approach to predicting the¹³C NMR chemical shifts of polysubstituted benzenes has been proposed (in the example case of compounds with substituents of one kind of the type C₆H_6–nX_n). The collective interactions of several substituents X [X=CH₃, C₂H₅, iso-C₃H₇, CF₃, COOH, f, Cl, Br, Si(CH₃)₃] have been expressed in the framework of a regression treatment in terms of two-particle increments. The chemical shift of each carbon atom has been represented in the form of an equation containing 17 parameters. The calculation scheme can be transformed and expanded for use even in the calculation of the spectra of compounds not previously studied. The calculated shifts for some previously investigated compounds and some compounds not previously investigated have been presented. The error in reproducing chemical shifts is equal to 0.2–0.3 ppm (and may be as high as 0.8 ppm for only a few measurements).V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 2, pp. 62–71, March–April, 1991.     

Thermal decomposition of ulexite

The thermal decomposition of ulexite, NaCa[B₅O₆(OH)₆] · 5H₂O, monocrystals was investigated by thermal, X-ray, IR and optical microscopy methods at normal and elevated temperatures.It was found that the thermal decomposition has an intraframework character and proceeds in a few separate stages: 1) release of part of the molecular water coordinating the Ca and Na cations; this leads to a rearrangement of the ulexite structure; 2) release of the remaining molecular water and some part the OH groups, which causes breakdown of the ulexite structure, with the simultaneous crystallization of CaO · B₂O₃ and 2CaO·B₂O₃; 3) the slow release of the remaining OH groups up to 600°C, which causes decomposition of the borate rings and the crystallization of NaB₃O₅ and NaCaBO₃.

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Zusammenfassung Mittels thermischer, röntgenographischer, IR- und optisch mikroskopischer Verfahren wurde bei Normal- und bei hohen Temperaturen die thermische Zersetzung von Ulexiteinkristallen NaCa[BsO₆(OH)₆]·5H₂O untersucht.Die Untersuchungen zeigten, daß die thermische Zersetzung von Ulexit einen Innergittercharakter trägt und in einigen separaten Schritten verläuft: 1) Freisetzung desjenigen molekularen Wassers, welches Ca und Na Kationen koordiniert; hierdurch geschieht eine Wiederherstellung der Ulexit-struktur, 2) Freisetzung des verbleibenden Kristallwassers und einem Teil der OH-Gruppen, wodurch eine Zersetzung der Ulexit-struktur unter gleichzeitiger Kristallisation von CaO · B₂O₃ und 2CaO · B₂O₃ erfolgt, 3) langsame Freisetzung der verbleibenden OH-Gruppen bis 600°C, was eine Spaltung der Boratringe und die Kristallisation von NaB₃O₅ und NaCaBO₃ zur Folge hat.

     

Crystal and molecular structure of hexacarbomethoxycyclopropane

A. N. Nesmeyanov Institute of Heteroorganic Compounds, Academy of Sciences of the USSR. N. D. Zelinskii Institute of Organic Chemistry, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 3, pp. 171–173, May–June, 1989.     

IR spectroscopic study of substituent effects in N,N-dimethylhydrazides of aromatic acids

Conclusions An IR spectroscopic study showed that the C=0 values in the spectra of N,N-dimethylhydrazides of aromatic acids, RCONHN(Me)₂, correlate linearly with a regression equation obtained for the unsubstituted hydrazides of aromatic acids, RCONHNH₂. This dependence differs significantly from that for N-methyl-N-aroylhydrazines, in which ,-conjugation in the RC(O)N group is more pronounced.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2353–2355, October, 1987.     

The crystal structure and absolute configuration of the antitumor platinum complex trans(OH)-Pt(OH)2(malonato)(1R,2R-cyclohexanediamine).

The absolute configuration of the anti-tumor complex trans(OH)-Pt(OH)2(malonato)(1R,2R-cyclohexanediamine) was determined by X-ray anomalous scattering technique. The final unit cell was monoclinic, space group P2(1) with a = 9.142 A, b = 7.788 A, c = 11.946 A, beta = 96.48 degrees, Z = 2. The crystal structure was determined by direct method and difference Fourier synthesis, and refined to R = 0.025 and Rw = 0.033 based on 2768 independent reflections. The platinum atom has roughly octahedral coordination. The cyclohexane ring has the expected chair configuration, with two amino groups in equatorial positions while the malonato ligand, in contrast, shows a boat conformation for six membered Pt O-C-C-C-O ring.     

Phospholipids of kenaf of variety Opytnyi-1847

The total phospholipids of kenaf of variety Opytnyi-1847 and homogeneous fractions of them have been studied. A known law has been confirmed — positions 2 of the main fractions of phospholipids are esterified predominantly with unsaturated fatty acids and in N-aceylated phospholipids the amide-bound acids are more saturated than the O-acyls.Institute of the Chemistry of Plant Substances of the Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 775–777, November–December, 1980.     

Effects of stereoisomerism in the mass spectra of 2,4-disubstituted thiacyclohexanes

The mass spectra of cis- (Ia-c) and trans-2-methyl-4-R-thiacyclohexanes (IIa-c; a R = n-C₄H₉, b R = n-C₅H₁₁, c R = Ph) were studied. It was established that [M-CH₃]⁺ ions, which correspond to the loss of a methyl group from the 2 position, are formed more readily in the case of the less stable trans isomers IIa-c than in the case of cis isomers Ia-c. The three-dimensional structures of the substances have no effect on the degree of elimination of the R substituent. The relative ionization energies (RIE) for Ia,b and IIa,b and the relative appearance energies (RAE) of the [M-CH₃]⁺ ions were measured by the electron impact method. It was found that the RIE are almost 0.05 eV lower and that the RAE of the [M-CH₃]⁺ ions are 0.1 eV lower for trans isomers IIa,b than for cis isomers Ia,b.Communication 4 from the series Ionization and appearance energies in organic chemistry, See [1] for Communication 3.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 333–338, March, 1981.     

Methylation analysis in glycoprotein chemistry. General procedure for quantification of the products of solvolysis of permethylated glycopeptides and glycoproteins

A technique for the gas chromatographic analysis of the products of solvolysis of permethylated glycopeptides and glycoproteins has been developed. It involves methanolysis of a permethylated compound, quantitative transformation of methyl ethers of methyl glycosides into the corresponding O-trimethylsilyl(TMS)-O-methylalditols [2-deoxy-2-(N-methyl)acetamido-O-TMS-O-methylalditols in the case of hexosamine derivatives] and gas chromatographic quantification using a single column packed with 0.4% OV-225 on surface-modified Chromosorb.     

Thermal stability of osmium mixed oxides. III. SrOsO3 decomposition products: A new defect pyrochlore Sr2Os2O6.4±0.2

The thermal decomposition of SrOsO₃ has been studied by DTA, thermogravimetry and X-ray powder diffraction. The decomposition of orthorhombic Sr₂Os₂O₇ depends strongly on the partial pressure of air above the samples investigated. In this paper the Sr₂Os₂O_6.4±0.2 pyrochlore formation and some properties of the phase are described. The stability conditions of SrOsO₃ are also discussed.     

The gas chromatography, thermal analysis and mass spectrometry of fluorinated lead β-diketonates Determination of traces of lead by the integrated ion-current technique

Preparative details for perfluoroalkanoylpivalylmethanes and their lead chelates are given. Thermal analysis, gas chromatography and mass spectral studies all indicate high thermal stability, but strong column interaction makes successful quantitative gas chromatography difficult. The integrated ion-current technique is applied to determine lead heptafluorobutanoylpivalylmethanate in the range 10^-9–10^-7 g of lead, but a lower detection limit of ca. 10^-14 g is indicated.