Die Hydrohalogenierung von Hexaphenyldigerman und die Schwingungsspektren einiger Ge2(C6H5) n X6−n -Verbindungen

The reactions of Ge₂(C₆H₅)₆ with HCl and HBr lead in nearly quantitative yields to the 1,1,2,2-tetrahalo derivatives Cl₂(C₆H₅)GeGe(C₆H₅)Cl₂ (I) and Br₂(C₆H₅)GeGe(C₆H₅)Br₂ (II), resp. The Si?Ge bond of (C₆H₅)₃SiGe(C₆H₅)₃ is cleaved under the conditions of hydrohalogenation. The vibrational spectra of Ge₂Br₆, Ge₂(C₆H₅)₆, I, and II are reported. The influence of vibrational coupling on ν GeGe in these compounds is discussed in detail, including vibrational calculations.     

New symmetry properties of a class of Hubbard models

In the Hubbard model for crystals of the AB-type all information on the system is already contained in the set of eigenstates where the number of sites equals the number of electrons or exceeds it by one. We prove this by deriving relations among the eigenstates with different numbers of particles which do not rely on the well-known transformation of electrons to holes. In this context a new good quantum number is identified. We report on results for the one-dimensional case.     

13 C 183W-Kopplungen als sonde für metall—carbin-, —carbenund—alkyl-bindungen

Carbon-13 NMR data are reported for trimethyltin derivatives containing ER_n groups where E  C, Si, Ge, Sn, N, O and S including a series of cyclic amines with ring sizes from three to seven. Coupling constant values for the homologous series of fourth group derivatives give goood correlations with the electronegativity of E. The observation of the two-bond, ¦ ²J(¹¹⁹SnE¹³C) ¦ couplings only in the derivatives containing bulky R groups is rationalized by a bimolecular exchange of ER_n groups in the concentrated solutions studied.     

Tailor-made functionalization of silicon nitride surfaces

This communication presents the first functionalization of a hydrogen-terminated silicon-rich silicon nitride (Si3Nx) surface with a well-defined, covalently attached organic monolayer. Properties of the resulting monolayers are monitored by measurement of the static water contact angle, X-ray photoelectron spectroscopy (XPS), and infrared reflection absorption spectroscopy (IRRAS). Further functionalization was performed by reaction of Si3Nx with a trifluoroethanol ester alkene (CH2=CH-(CH2)8CO2CH2CF3) followed by basic hydrolysis to afford the corresponding carboxylic acid-terminated monolayer with hydrophilic properties. These results show that Si3Nx can be functionalized with a tailor-made organic monolayer, has highly tunable wetting properties, and displays significant potential for further functionalization.     

Splitless on-line coupling of capillary high-performance liquid chromatography,capillary electrochromatography and pressurized capillary electrochromatography with nuclear magnetic resonance spectroscopy

A mixture of unsaturated fatty acid methyl esters was separated with a new splitless capillary set-up. With the employed apparatus configuration different capillary separation techniques such as capillary high-performance liquid chromatography (cHPLC), capillary electrochromatography (CEC) and pressurized capillary electrochromatography (pCEC) could be applied. The detection and identification of the sample compounds were accomplished by hyphenating these capillary separation techniques with nuclear magnetic resonance (NMR) spectroscopy using a novel configuration of the detection capillary set-up. Using modified electrokinetically driven separation techniques, the electric field was applied solely across the separation column. With this improved interface for capillary liquid chromatography-NMR on-line coupling, the stereochemical assignment of the cis and trans configuration of unsaturated fatty acids could be easily accomplished. Finally, the results of cHPLC-NMR, CEC-NMR and pCEC-NMR coupling experiments were compared.Dedicated to Professor Günter Häfelinger on the occasion of his 65th birthday     

Capillary zone electrophoresis in non-aqueous solutions: pH of the background electrolyte

Although the establishment of a pH scale and the determination of the pH in water is not problematic, it is not a straightforward task in non-aqueous solvents. As capillary zone electrophoresis (CZE) in organic solvents has gained increasing interest, it seems to be valuable to re-discuss the concept of the pH in such media, especially pointing to those aspects, which make pH measurement uncertain in non-aqueous solvents. In this review, the relevant aspects when dealing with primary standard (PS) and secondary standard (SS) as recommended by the International Union of Pure and Applied Chemistry (IUPAC), and the usage of the operational pH are discussed with special emphasis to non-aqueous solvents. Here, different liquid junction potentials, incomplete dissociation of the electrolytes (especially in solvents with low or moderate relative permittivity) and the occurrence of homo- and heteroconjugation must be taken into account. Problems arising in capillary zone electrophoresis practice are addressed, e.g. when the background electrolyte (BGE) consists of organic solvents, but the measuring electrode (normally the glass electrode) is calibrated with aqueous buffers, and the liquid junction potentials between the solvents do not cancel each other. The alternative concept of establishing a certain pH is described, using mixtures of reference acids or bases with known pKa in the organic solvent, and their respective salts, at a certain concentration ratio, relying to the Henderson-Hasselbalch equation. Special discussion is directed to those organic solvents most common in capillary zone electrophoresis, methanol (MeOH) and acetonitrile (ACN), but other solvents are included as well. The potential significance of small amounts of water present in the organic solvent on changes in pKa values, and thus on the pH of the buffering components is pointed out.     

Contribution to the quantitative x-ray analysis of individual submicrometre particles: Asbestos fibres

Summary A procedure for the analysis of individual asbestos fibres in the submicrometre diameter range, based on the ratio method of thin film analysis, is presented. The reliability of this method has been tested in a study of identification of asbestos fibres. The systematic and statistical errors were investigated.

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Beitrag zur quantitativen Röntgenmikroanalyse einzelner Submikrometerteilchen: Asbestfasern

Zusammenfassung Es wurde versucht, eine Quantifizierungsmethode analog der Verhältnismethode zur Analyse dünner Schichten für die Analyse von Asbestfasern mit Durchmessern im Submikrometerbereich zu entwickeln. Die Zuverlässigkeit der Methode wurde mit einem Anwendungsbeispiel überprüft, und alle systematischen und statistischen Fehler wurden dargelegt.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

In-situ deactivation of packed columns for SFC

Residual adsorptive activity of reversed phase (RP) column packings used in supercritical fluid chromatography (SFC) can be significantly reduced by a dynamic in-situ silanization with diphenyltetramethyldisilazane (DPTMDS). RP-materials thus deactivated were characterized both chromatographically and by solid-phase ²⁹Si NMR.     

2D-NMR: Part VI. 2D-INADEQUATE spectral analysis and crystal structure of tricyclo[7.3.1.02,7]tridecane

2-Hydroxy-13-oxo-tricyclo[7.3.1.0^2,7]tridecane derivatives can be obtained by reaction of cyclohexanone with alcohols under alkaline conditions. The unambiguous assignment of all signals of the¹H-NMR- and¹³C-NMR-spectrum is possible by 2D-¹H-¹³C-shift correlation and 2D-INADEQUATE. Compound1 crystallizes in space group P2₁/n witha=8.518 (1),b=14.789 (2),c=19.321 (2) Å, =94.91 (1)°,Z=8,D _c =1.22 Mg cm^–3. The structure refined toR=0.100 andR _w =0.097 for 1719 observed reflections. Two independent molecules form centrosymmetric hydrogen-bonded dimers.Part V:Haslinger E.,Kalchhau-ser H.,Robien W.,Steindl H., Monatsh. Chem.115, 597 (1984).