Chemistry of the phenoxathiins and isosterically related heterocycles. XVI. The synthesis and molecular structure of 3-azaphenoxathiin: Evidence in support of factors responsible for control of the dihedral angle

The synthesis of the 3-azaphenoxathiin ring system and its molecular structure are reported. Based on ¹³C-nmr chemical shift additivities associated with the insertion of an annular nitrogen atom and the observed ¹³C-nmr shift of Cα, the title compound was predicted to have a dihedral angle θ = 160.2°. The observed dihedral angle from the crystal structure was found to be θ = 167.07° which is in reasonably good agreement with the predicted value. It is proposed that the position of the annular nitrogen atom is solely in-control of the observed dihedral angle.     

Capillary electrophoresis of methyl-substituted phenols in acetonitrile

The separation of mono- and dimethylphenols by capillary electrophoresis in pure acetonitrile was investigated. In acetonitrile, uncharged phenols interact with background electrolyte anions forming negatively charged complexes, which can be separated from each other by capillary electrophoresis. The background electrolyte anions tested were acetate, bromide and chloride. The calculated formation constants for phenol–anion complexes were highest with acetate and smallest with bromide. Complex formation was found to be sensitive to traces of water in the background electrolyte. The separation of methylphenols was also carried out in acetonitrile at high pH using background electrolytes prepared from diprotic acids and tetrabutylammonium hydroxide. At high pH the phenols were partly dissociated, providing an additional mechanism for the separation. All methylphenols were separated with the use of malonate background electrolyte. However, this approach was prone to interference from methanol resulting from the tetrabutylammonium hydroxide solution.     

The relevancy of the [B2N4] substructure in the electronic structure of the metal-rich lanthanum nitridoborate La3(B2N4)

Lanthanoide nitridoborates of the general formula Ln₃(B₂N₄) with Ln=La, Ce, Pr, and Nd occur as black crystalline materials. Their structures contain oxalate-like [B₂N₄]⁸⁻ ions being stacked in an eclipsed formation along one crystallographic direction. Electronic structures were calculated for a molecular [B₂N₄]⁸⁻, for the [B₂N₄] partial structure, and for the complete La₃(B₂N₄) structure with the extended Hückel algorithm to analyze the bonding characteristics and to trace the necessity and properties of one surplus electron of (La³⁺)₃(B₂N₄⁸⁻)(e⁻). The HOMO of a [B₂N₄]⁸⁻ is B-B σ bonding, and the LUMO is B-B π bonding but B-N antibonding. The energy band of the solid state [B₂N₄] partial structure corresponding to the LUMO is broadened as a result of intermolecular B?B interactions between adjacent [B₂N₄] units along the stacking direction. Due to bonding interactions with La d orbitals, this band is significantly lowered in energy and occupied with one electron in the band structure of La₃(B₂N₄). This singly occupied band exhibits no band crossings but creates a semimetal-like band structure situation.     

Directed 1,3-dipolar cycloadditions of ylidene piperazine-2,5-diones

The reactivities and selectivities of 1,3-dipolar cycloaddition reactions of ylidene piperazine-2,5-diones with mesitonitrile oxide are reported. The stereoselectivities of reactions with chiral ylidene piperazine-2,5-diones can be directed by judicious choice of substituents on the N- and/or C-substituents of the piperazinedione ring.     

Rapid detection of hydroxyl groups on solid-phase

A rapid method for the qualitative detection of hydroxyl groups on solid-phase has been developed. The method employs N-methylisatoic anhydride to derivatise resin-bound substrates possessing free hydroxyl functionality. The resultant fluorescent ester can be detected by visualisation under a standard laboratory UV lamp at 365 nm excitation.     

The behaviour of perchloro-3,4-dimethylenecyclobutene,-pentafulvene and- pentafulv-alene under electron-impact

The mass spectra of 1,2-dichloro-3,4-bis(dichloromethylene)cyclobutene (IV) and of hexachloropentafulvene (II) have been studied. Compound IV cannot be an intermediate in the formation of II from octachloro-1,2-dimethylenecyclobutane (III) under electron-impact, as previously suggested. In the mass spectra of II and IV the species [C₆]⁺ and [C₅]⁺ occur, obviously through cleavage of the semicyclic C-C bond. The mass spectrum of pentachlorofulvalene (VI) shows strikingly that successive elimination of an even number of CI atoms is preferred over that of an odd number of CI atoms; probably corresponding C-CI bonds in the two rings are broken simultaneously. Amongst the fragments, the species [C₁₀]⁺ and [C₇]⁺ and possibly also [C₈]⁺ and [C₉]⁺ have been observed.     

The determination of UO2 and UO3 in different layers of a single crystal of uraninite

Summary The authors have performed analyses on different layers of a single uraninite crystal, a cleveite from Auselmyren, Aust-Agder, Norway. The separation of the layers having been made by mechanical means, it was possible to determine the amount of uranous oxide in them.About 0,05 g. of mineral is brought into solution by heating with sulfuric acid and the UO₂ content determined by titration with 1/100 n. permanganate-solution. The liquid is then reduced in aJones reductor and another titration gives the entire amount of uranium. The ratio UO₂/UO₃ can then be deducted.It is highest in the core, diminishing gradually towards the outside. The same is found also for the UO₂ content, while the amount per cent. of UO₃ is highest in the outside layer and lowest in the core.

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Zusammenfassung Die beiden Autoren haben Analysen in den verschiedenen Schichten eines einzelnen Uraninitkristalles — Cleveit aus Auselmyren, Aust-Agder, Norwegen — durchgeführt. Nach Trennung der Schichten auf mechanischem Wege war es möglich, die Mengen von Urano-Oxyd in jeder gesondert zu bestimmen.Ungefähr 0,05 g Mineral werden durch Erhitzen mit Schwefelsäure in Lösung gebracht und der Urandioxydgehalt wird durch Titration mit 1/100 n-Permanganatlösung bestimmt. Die Lösung wird dann im Reduktor nachJones reduziert und eine neuerliche Titration ergibt die Gesamtmenge des Urans. Daraus läßt sich das Verhältnis UO₂:UO₃ ableiten.Dieser Quotient ist am höchsten im Innern des Minerals und nimmt gegen die äußeren Schichten stetig ab. Dasselbe Verhalten zeigte der Urandioxydgehalt, während der perzentuelle Gehalt an Urani-Oxyd am größten in den äußeren Schichten und am kleinsten in den inneren ist.

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Résumé Les auteurs ont effectué l'analyse des différentes souches d'u d'un seul cristal d'uraninite — une clévéïte d'Auselmyren, Aust-Agder, Norvège. Les souches ayant été séparées mécaniquement, on parvint à doser leur teneur en oxyde uraneux.0,05 g. près, du minéral ont été dissous, à chaud, dans de l'acide sulfurique et la teneur en dioxyde d'uranium fut dosée par titrage avec de la solution 0,01 n de permanganate.Enfin, la solution est réduite dans un réducteurJones et un nouveau titrage donne la quantité totale d'uranium. On trouve, de cette façon, la proportion de UO₂:UO₃.Ce quotient est le plus élevé au centre du cristal et va décroissant continuellement vers la surface. Il en est de même quant à la teneur du dioxyde d'uranium, tandis que le pourcentage de UO₃ est le plus élevé dans la souche superficielle et le plus bas dans le centre du cristal.

     

INDO MO calculations of the electronic structures of pyrolle,imidazole, and derivatives

INDO MO calculations on a series of N-substituted pyrroles and imidazoles have been analysed for substituent effects. Some of the basic characteristics of the σ_I and σ_R⁰ parameters are reflected in the calculated electron densities of the compounds studied. For example, good correlations are obtained between Δqσ ^N(1)/ΣΔqσ parameters and σ_I for the R substituted compounds, as well as between ΣΔqπ values and σ_R⁰ for the + R derivatives. The + R substituents lead to an increased localization of the π-bonds, whereas R substituted derivatives show an increased delocalization, i.e., the π-bond orders across C(2)C(3) [or C(2)N(3)] and C(4)C(5) decrease and those across other bonds in the ring increase.     

Formation constants and oxidation of bis(1,10-phenanthroline)-copper(I) perchlorate and bis(2,2′-bipyridine)copper(I) perchlorate by molecular oxygen in formamide

Summary A study was made of the slow oxidation with molecular oxygen in formamide of the cuprous complexes Cu(1,10-phenanthroline)₂ ⁺ and Cu(2,2-bipyridine)₂ ⁺, and of Cu(MeCN)₄ClO₄ with and without complexing agents. The two formation constants were calculated from the kinetic data. Both complexes reacted with a rate constant of 0.001 with respect to the value obtained in solvent water. A catalytic effect of the water molecules is proposed to explain this difference. The cupric complexes formed were isolated and identified as [CuL₂ formate]ClO₄ and [CuL₂ cyanate]ClO₄.