Are the NF4+ cations in NF4BF4 really nontetrahedral?

The crystal structure of NF4BF4 has been reexamined. The low-temperature X-ray structure and solid-state 19F MAS NMR spectra are in agreement with the conclusions reached from the vibrational spectra, that solid NF4+ salts contain only tetrahedral NF4+ cations. The alleged observation of two kind of nontetrahedral NF4+ cations in several previous crystal structures is attributed to incorrectly solved structures and, possibly, problems caused by disorder or twinning. It is further evidence for the dangers of over-reliance on crystal structures. Flawed crystal structures can give rise to either bad or unwarranted theory.     

Phase Equilibria in the System YPO4–K3PO4–KMgPO4

The phase equilibria in the part of the ternary system YPO₄–K₃PO₄–Mg₃(PO₄)₂ over the composition range YPO₄–K₃PO₄–KMgPO₄ were examined and determined by differential thermal analysis, X-ray powder diffraction and microscopic analysis in reflected light. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phase equilibria in the ErPO4–K3PO4 system

The phase equilibria occurring in the ErPO₄–K₃PO₄ system were investigated by the thermal analysis, FTIR, and X-ray powder diffraction methods. On the basis of obtained results, the related phase diagram is proposed. This system includes one intermediate compound, K₃Er(PO₄)₂; the double phosphate melts incongruently at 1355 °C and occurs in two polymorphic forms; transformation β/α-K₃Er(PO₄)₂ proceeds at 420 °C. The eutectic occurs at the composition of 58.5 wt% K₃PO₄, 41.5 wt% ErPO₄ at 1317 °C.     

Effect of the Composition of the Aqueous Organic Solvent on the Kinetics of N-Acylation of α-Amino Acids with 4-Nitrophenyl 4-Nitrobenzoate

Equations relating the N-acylation rate constants of glycine, L--alanine, DL-threonine, and L-proline with 4-nitrophenyl 4-nitrobenzoate in water-acetonitrile, water-2-propanol, and water-2-methyl-2-propanol solvents to the composition of the medium were obtained, and reaction rate constants in water were calculated.     

Phase equilibria in the YPO4–Rb3PO4 system

The phase equilibria occurring in the YPO₄–Rb₃PO₄ system were investigated by thermoanalytical methods, X-ray powder diffraction, and ICP-OES. On the basis of the obtained results, its phase diagram is proposed. It was found that the system includes two intermediate compounds Rb₃Y(PO₄)₂ and Rb₃Y₂(PO₄)₃. The Rb₃Y(PO₄)₂ compound melts congruently at 1300 °C. The Rb₃Y₂(PO₄)₃ orthophosphate was previously unknown. This intermediate compound is high-temperature unstable and decomposes within the temperature range 1300–1330 °C to YPO₄ and Rb₃Y(PO₄)₂. The decomposition process is irreversible. It was found that the Rb₃Y₂(PO₄)₃ orthophosphate is isostructural with Rb₃Yb₂(PO₄)₃ and crystallizes in the cubic system (a = 1.70226 nm).     

IR spectroscopic study of the conformational lability of 4′-ethyl-4-cyanobiphenyl

The conformational lability of 4-ethyl-4-cyanobiphenyl molecules in solid crystal (SC) and isotropic liquid (IL) states was investigated by IR spectroscopic techniques (experiment and theory). IR absorption spectra were measured at 28°C–95°C in the frequency range 400 cm^–1–4000 cm^–1. Spectrum simulation was performed using the fragment method with allowance for the conformational fluctuations of molecules. The experimental and calculated spectra were compared and analyzed, and it was shown that in the IL, the samples are mixtures of conformers. The temperature changes in the spectra in the stated range are caused by the conformational lability of molecules.Original Russian Text Copyright © 2004 by L. M. Babkov, I. I. Gnatyuk, G. A. Puchkovskaya, and S. V. TrukhachevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 398–405, May–June, 2004.     

Investigations of the thermal stability and phase transformations in the system marocco phosphorite—(NH4)3H(SO4)2.NH4HSO4

Different physical chemical methods were used to study the thermochemical processes in a system involving a natural phosphate and complex acid salts of ammonium sulphate. The products of decomposition of the double ammonium salt and the products of their interactions with the phosphate were identified. The formation of ammonium and calcium polyphosphates and the disproportionation of P₃O ₁₀ ^5? and P₂O ₇ ^4? to PO ₄ ^3? and PO ₃ ^? were found to depend on the circumstances of the thermal interactions.     

A vibrational analysis of the MnO 4 − bands

Teltow'S [14,15] measurements of the permanganate bands are reanalyzed using the level scheme of Ballhausen and Liehr [2]. For KMnO ₄ dissolved in KClO ₄ the components of the first ¹ T ₂ state are found at 18050 cm^–1 18078 cm^–1 and 18043 cm^–1. The breathing frequency of the MnO _– ⁴ unit is in this state 768 ^–1. The electronic origin of the second ¹ T ₂ state is found at 30723 cm^–1 with a breathing frequency of 760 cm^–1.Evidence is further found for a ¹ T ₁ state with its split components located at 14446 cm^–1, 14526 cm^–1 and 14600 cm^–1. The breathing frequency is here found to be 800 cm^–1.Finally for KMnO ₄ dissolved in NaClO ₄ there are indications that one or two spin-triplets are located near 13200 cm^–1.

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Zusammenfassung TeltowS Messungen des Permanganatspektrums [14, 15] werden mit Hilfe des Termschemas von Ballhausen und Liehr [2] von neuem analysiert. Für KMn ₄ in KClO ₄ findet man die zum ersten ¹ T ₂-Zustand gehörenden Komponenten bei 18050, 18078 und 18043 cm^–1. Die Valenzschwingung des MnO _– ⁴ liegt hier bei 768 cm^–1. Der Ursprung des zweiten ¹ T ₂-Systems wird bei 30723 cm^–1 gefunden, die dazugehörige Valenzfrequenz ist 760 cm^–1.Bei 14446, 14526 und 14600 cm^–1 liegen offenbar die Komponenten eines ¹ T ₁-Terms, wozu eine Valenzfrequenz von 800 cm^–1 gehört.Schließlich findet man für KMnO ₄ in NaClO ₄ Anzeichen für ein oder zwei Spin-Tripletts um 13200 cm^–1.

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Résumé Les bandes d'absorption du permanganate, mesurées par Teltow [14,15], sont réanalysées à l'aide d'un système de termes proposé par Ballhausen et Liehr [2]. Pour KMnO ₄ dans KClO ₄, on trouve les composants du premier état ¹ T ₁ à 18050, 18078 et 18043 cm^–1. La vibration symétrique du MnO _– ⁴ dans cet état se situe à 768 cm^–1. L'origine électronique du second état ¹ T ₂ est trouvé à 30723 cm^–1, la fréquence oscillatrice correspondante est de 760 cm^–1.Un état ¹ T ₁ avec ses composants à 14446, 14526 et 14600 cm^–1 est mis en évidence, avec une vibration symétrique de 800 cm^–1.Finalement, au cas du KMnO ₄ dissous dans le NaClO ₄, il y a des indications pour un ou deux triplets de spin vers 13200 cm^–1.

     

The thermodynamic stability of the LaBr 4 − ion

The thermodynamic stability of the LaBr ₄ ^? anion was for the first time studied by high-temperature mass spectrometry and nonempirical quantum-chemical methods. The experimental and theoretical enthalpies of the reaction $ LaBr_4^ - = Br^ - + LaBr_3 The thermodynamic stability of the LaBr₄⁻ anion was for the first time studied by high-temperature mass spectrometry and nonempirical quantum-chemical methods. The experimental and theoretical enthalpies of the reaction were Δ_r H°(298.15 K) = 302 ± 14 and 303 kJ/mol, respectively. The value Δ_f H° (LaBr₄⁻, g, 298.15 K) = −1105 ± 14 kJ/mol was recommended as the enthalpy of formation of the LaBr₄⁻ anion. Original Russian Text ? M.F. Butman, L.S. Kudin, V.B. Motalov, D.A. Ivanov, V.V. Sliznev, K.W. Kr?mer, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 5, pp. 885–890.     

Lithium-cationic conductivity in the Li4 − 2x Cd x GeO4 system

The lithium-conducting solid electrolytes in the Li_{4 ? 2x} Cd _x GeO₄ (0 ≤ x ≤ 0.6) system are synthesized. Their crystal structure and temperature and concentration dependences of conductivity are studied. The specimens with the highest conductivity have a γ-Li₃PO₄-derivative structure. The solid solutions with x = 0.15–0.25 are stable at the room temperature, whereas the specimens with x ≥ 0.3 decompose yielding Li₂CdGeO₄ below 310 ± 10°C. Li_3.6Cd_0.2GeO₄ solid solution exhibits the highest conductivity (5.25 × 10^?2 S cm^?1 at 300°C). The factors, which affect the conductivity of synthesized solid electrolytes, are considered.     

Structural variations of N-acetylneuraminic acid,part 19: Synthesis of both epimeric pairs of the 4-C-methyl- and 4-deoxy-4-C-methyl- as well as of the β-methylketoside of 4-deoxy-4-C-methylene-N-acetylneuraminic acid

Summary While the reaction of the 4-oxo-Neu 5 Ac derivative2 a with tributoxy methyl zirconate led exclusively to equatorial 4-C-methyl derivative3 a, the analogous reaction with tetramethyl zirconate yielded a 3:2 mixture of both diastereoisomeres3 a and4 a. After removal of protecting groups the 5-acetamido-3,4-dideoxy-4-C-methyl-D-glycero-D-galacto-2-nonulosonic acid5 a and 5-acetamido-3,4-dideoxy-4-C-methyl-D-glycero-D-talo-2-nonulosonic acid6 a were obtained. The 4-C-methylene derivative was prepared by treatment of the same 4-oxo-derivative with CH₂I₂/Zn/Cp ₂ZrCl₂. Subsequent hydrogenation led to both epimeric 4-deoxy-4-C-methyl derivatives8 a and9 a. Final removal of protecting groups gave the 5-acetamido-3,4,5-trideoxy-4-C-methyl-D-glycero-D-galacto-2-nonulosonic acid10 a respectively the 5-acetamido-2,7-anhydro-4-C-methyl-3,4,5-trideoxy-D-glycero-D-talo-2-nonulosonic acid11 a. The -methylketosides of the 4-deoxy-4-C-methyl- (16) and 4-C-methylene-Neu 5 Ac (15) were prepared via the peracetylated derivatives to obtain modell substrates for enzymatic studies. Thus all free acids were tested for inhibition of CMP-sialate synthease. Only the 4-C-methylene compound15 showed most unexpectedly a strong competitive inhibition of this enzyme.

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Strukturelle Abwandlungen an N-Acetylneuraminsäure, 19. Mitt.: Synthese der beiden Epimerenpaare der 4-C-Methyl- und 4-Deoxy-4-C-methyl- sowie des -Methylketosids der 4-Deoxy-4-C-methylen-N-acetylneuraminsäure. Verhalten gegenüber CMP-Sialat-Synthase

Zusammenfassung Während die Umsetzung des 4-Oxoderivates2 a mit (BuO)₃ MeZr ausschließlich zur equatorialen 4-C-Methylverbindung3 a führt, wurde bei der Reaktion mitMe ₄Zr ein 3:2-Gemisch der beiden Diastereomeren3 a und4 a erhalten. Das 4-C-Methylenderivat7 a wurde durch Reaktion derselben 4-Oxoverbindung mit CH₂I₂/Zn/Cp ₂ZrCl₂ erhalten. Eine anschließende Hydrierung (H₂-Pd/C) führte zu einem trennbaren Germisch der beiden 4-Deoxy-4-C-methylderivative8 a und9 a. Diese Verbindungen konnten durch das Entfernen der Schutzgruppen einerseits in die 5-Acetamido-3,4,5-trideoxy-4-C-methyl-D-glycero-D-galacto-2-nonulosonsäure10 a und 5-Acetamido-2,7-anhydro-4-C-methyl-3,4,5-tridoxy-D-glycero-D-talo-2-nonulosonsäure11 a umgewandelt werden. Die Verbindungen Methyl-5-acetamido-4-C-methylen-3,4,5-trideoxy--D-manno-2-nonulopyranosidonat (15) und Methyl-5-acetemido-4-C-methyl-3,4,5-tridoxy--D-glycero-D-talo-2-nonulopyranosidonat (16) wurden als Modellverbindungen für enzymatische Untersuchungen über peracetylierte Zwischenstufen hergestellt. Überraschenderweise zeigte nur die 4-C-Methylenverbindung15 eine starke kompetitive Hemmung gegenüber CMP-Sialat-Synthase.

     

Synthesis and NMR spectroscopic conformational analysis of esters of 4-hydroxy-cyclohexanone—the more polar the molecule the more stable the axial conformer

The esters of 4-hydroxy-cyclohexanone and a series of carboxylic acids R–COOH with R of different electronic and steric influence (R=Me, Et, n-Pr, i-Pr, n-Bu, i-Bu, sec-Bu, t-Bu, CF₃, CH₂Cl, CHCl₂, CCl₃, CH₂Br, CHBr₂, and CBr₃) were synthesized and the conformational equilibria studied by ¹H and ¹³C NMR spectroscopy at 103 K and at 295 K, respectively. The geometry of optimized structures of the axial/equatorial chair conformers was computed at the ab initio MO and DFT levels of theory. Only one preferred conformation was obtained for the axial and the equatorial conformer as well. When comparing the conformational equilibria of the cyclohexanone esters with those of the corresponding cyclohexyl esters a certain polarity contribution of the cyclohexanone framework was revealed, which is independent of the substituent effects and increases the stability of the axial conformers by a constant amount.     

Experimental investigation of the formation of double phosphates in the LaPO4–NaF system

In the course of segregation smelting of rare-earth and rare metal raw materials with a fluxing agent (NaF), two immiscible melts form, one of which is a silicate melt and the other is a phosphate–salt melt. The silicate melt is enriched with Fe₂O₃, Al₂O₃, SiO₂, and Nb₂O₅, and the phosphate–salt melt is dominated by P₂O₅, TR₂O₃, Sc₂O₃, and Y₂O₃, and also with Ca, Sr, and Ba oxides. Chemical reactions between lanthanum orthophosphate and sodium fluoride in the LaPO₄–NaF system were studied for developing a technology for processing the phosphate–salt (rare-earth metal) melt. It was found that a metathesis reaction gives double phosphate Na₃La[PO₄]₂ and binary fluoride NaLaF₄. The products of crystallization of melts in the LaPO₄–NaF system decompose in weak mineral acids unlike those in conventional technology for processing monazite raw material.     

An investigation of the polythermal diagram of the H2ONa2HPO4Na2SO4 system

The polythermal diagram of the ternary system H₂ONa₂HPO₄Na₂SO₄ has been established, setting up nine isotherms obtained between 0 and 25°C by conductimetric analysis. The solubility domains of the various solid phases have been determined. One eutectic, three stable and one metastable transitional transformations have been observed. Temperature and composition of the eutectic point have been obtained by thermal analysis at constant flow.     

Structure of Dimers and the Nature of Color in 4′-Nitro-4-dimethylaminoazobenzene Solutions

A mechanism is proposed for the formation of stable dimers of 4′-nitro-4-dimethylaminoazobenzene dye (4′-nitro-DAB)₂ in solution, the existence of which in a vapor phase was established in 1965. It is shown that (4′-nitro-DAB)₂ dimers are stable also in neutral and moderately acidic solutions. Their UV–Vis spectra are similar to the spectra of the same solutions of 4-dimethylaminoazobenzene (DAB) containing DAB₂ dimers as the ground state. Like DAB₂, (4′-nitro-DAB)₂ dimers are reversibly converted to di- and triprotonated dimers under conditions of low and moderate acidity. In the process, the yellow color of the initial solution changes to red. It is concluded that the great stability of the dimers in the liquid and vapor phases is due to their inter-monomer bonds being formed with the participation of electrons promoted from the sp²- orbitals of N-atoms in azo-groups N=N to the Rydberg 3s-orbitals of the N=N-group (Rydberg bonds). It is established that at high acidities, the triprotonated dimers (the red solution) decompose reversibly into diprotonated monomers (the yellow solution). Structural formulas are proposed for the protonated species.     

Theoretical Study on the Reaction Mechanism of SiCl_4 with H in the Gas Phase

1 INTRODUCTION Semiconductor silicon materials are vital for mi- croelectronic and information industry. Silicon has many advantages, for example, rich resource, out- standing quality and sophisticated processing tech- nology. So it has been widely used in semiconduc- tor industry. One of the key techniques of mo- dern microelectronic industry is epitaxial growth of single crystal thin film on single crystal silicon and its ba- cking materials. In the chemical vapour deposition of Si, g…     

DFT Study on the Origin of the Enantioselectivity of （S）-4-Hydroxylproline-Catalyzed Direct Aldol Reaction between Acetone and 4-Nitrobenzaldehyde

DFT-B3LYP calculations were carried out to study the enantioselectivity of the （S）-4-hydroxylproline-catalyzed direct aldol reaction between acetone and 4-nitrobenzaldehyde. Four transition structures associated with the stereo-controlling step of the reaction have been determined. They are corresponding to the anti and syn arrangements of the methylene moiety related to the carboxylic acid group in enamine intermediate and the si and re attacks to the aldehyde carbonyl carbon. The effect of DMSO solvent on the stereo-controlling step was investigated with polarized continuum model （PCM）. The computed energies of the transition states reveal the moderate enantioselectivity of the reaction.     

NaIO_4-Catalyzed Bromination of the Aromatic Ring of Lappaconitine

Lappaconitine 1, a bisnorditerpenoid alkaloid, was isolated from many plants of Aconitum species such as A. barbatum var. pulerulum and A. sinomontanum (Ranunculaceae)1-3, and used clinically for treatment of analgic disease as a nonaddicted drug in China4, and as an antiarrythmic in Uzbekistan5. In order to search for high activity, low toxicity compounds, we have carried out the structure modifications of lappaconitine. In this case, an attempt to induce the oxygenated group at C-10 in 1 b…     

Esterification and Selective Esterification in the Presence of TiCl4

A series of carboxylic acids was esterified to the corresponding esters with TiCl_4 as catalyst at room temperature,in high yields.This catalyst was highly effective for the selective esterification of primary alcohols with carboxylic acids,in the presence of secondary alcohols,and for the selective esterification of saturated acid with alcohol in the presence of conjugated acid or aromatic acid.On account of the high yield,high chemoselectivity,mild condition,and being free of other dehydrants,this is an efficient method.