Technische Verfahren zur Synthese von Carotinoiden und verwandten Verbindungen aus 6-Oxo-isophoron. VI. Synthese Von Rhodoxanthin und (3-RS, 3′RS)-Zeaxanthin; Zugänge zur C15-Ringkomponente über 3-Oxo-jonon-Derivate

Technical Procedures for the Synthesis of Carotenoids and Related Compounds from 6-Oxo-isophorone, VI. Synthesis of Rhodoxanthin and (3RS, 3′RS)-Zeaxanthin; Routes to the C₁₅-Ring Component via 3-Oxo-ionone Derivatives The C₁₅-ring component 4 , key intermediate of a new scheme for the synthesis of rhodoxanthin ( 1 ) and (3RS, 3RS)-zeaxanthin ( 3 ), has been synthesized starting from 6-oxo-isophorone ( 7 ) via 3-oxo-cyclocitral and 3-oxo-ionone derivatives.     

Comparing weak versions of separability

Our aim is to investigate spaces with σ-discrete and meager dense sets, as well as selective versions of these properties. We construct numerous examples to point out the differences between these classes while answering questions of Tkachuk [22], Hutchison [13] and the authors of [7].     

FTIR Emission Spectra, Molecular Constants, and Potential Curve of Ground State GeO

Extensive new high-temperature, high-resolution FTIR emission spectroscopy measurements for the five common isotopomers of GeO are combined with previous diode laser and microwave measurements in combined isotopomer analyses. New Dunham expansion parameters and an accurate analytical potential energy function are determined for the ground X1Sigma+ state. Copyright 1999 Academic Press.     

Redoxkinetik von Metallkomplexen in nichtwäßrigen Lösungen,XI. Die Reduktion von Thallium(III)oxinat mit Eisen(II) in schwach koordinierenden Lösungsmitteln

The kinetics of the iron(II) reduction of thallium(III) oxinate does not differ essentially from that of the oxinate-transfer from thallium(III)-oxinate to iron(III), described before: formation of a binuclear intermediate, rearrangements within, and subsequent reaction with the excess reactant to the final products. As for the redox process, these intermediates are binuclear Tl(II)-Fe(III) complexes which, with initial reactants, form further complexes in which the second electron is transferred. In the cases of excess Tl(ox)₃ and of equimolar reactants, disproportionations are likely involved.     

Contribution to the application of the langmuir probe technique for plasma monitoring in the Ar and n-hexane mixture plasma during the polymerisation process

In the present paper the Langmuir probe technique was applied for plasma monitoring in the Ar and n-hexane mixture plasma during the polymerisation process. The experiments were performed in a stainless steel DC magnetron reactor with a planar magnetron cathode. Within the investigated range of the gas pressure, no time-stable condition of the discharge was found. The regular oscillations, of a frequency of approximately 32 kHz, were observed in the Ar and 20% n-hexane mixture at the total pressure of 10 Pa and the discharge current of 8 mA. The experimentally obtained probe characteristics were used to determine the density and the average energy of electrons. In the DC magnetron stainless steel reactor the electron average energy in the Ar and n-hexane mixture plasma was about one order of magnitude smaller than in the case in which the working gas inside the reactor was the pure Ar. The probe measurements in the magnetron reactor were supplemented by the experiment in the customary glass discharge tube with a hollow cathode. In the glass discharge tube and in the Ar and 10% n-hexane mixture plasma a region of plasma parameters was found, in which the plasma was stable and no instabilities were observed. At such conditions the experiments in the glass discharge tube were used for the study of the efficiency of the probe surface cleaning methods used. This report was financially supported by grant 202/97/1011, 202/98/0116 and 202/98/0666 of the Grant Agency of Czech Republic, by the grant 75/98 of the Grant Agency of Charles University and by project COST 516. This work has been done within the framework of Association for Education, Research and Application in Plasma Chemistry.     

Accurate and stable numerical Hartree–Fock calculations for atoms. I. The 1s2 ground state of H−, He,Li+, and Be++

New techniques have been developed for atomic self-consistent-field calculations by numerical integration. For the origin and tail regions we present analytical expansions which can represent the solutions to high accuracy. For the numerical integration in the central region a five-point generalization of the Numerov formula is used; the error term is of the order h¹⁰. While this formula is unstable if used in the customary way, stability is achieved by using a Gaussian elimination technique. The new procedures are tested on the ground state of the helium isoelectronic series; with 251 integration points all quantities are calculated with an inherent accuracy of better than 10^–11.     

Cyclotrimerisierung von Ferrocenderivaten: Triferrocenyl-benzole

Zusammenfassung Cyclotrimerisierung von Ferrocenylacetylen und seinen Derivaten führt unter verschiedenen Bedingungen ausschließlich zu 1,2,4-Triferrocenyl-benzolen. Davon ist besonders die glatte Trimerisierung bei der rein thermischen Behandlung von Ferrocenyl-bzw. Methylferrocenylacetylenen bemerkenswert. Optisch aktives (-Methylferrocenyl)-acetylen liefert dabei ein stark aktives 1,2,4-Tri-(-methylferrocenyl)-benzol. Aus Ferrocenyl-methyl-bzw. Ferrocenyl-phenyl-acetylen erhält man bei Verwendung von Co₂(CO)₈ als Katalysator die sterisch stark überladenen (unsymm.) Trimethyl- bzw. Triphenyl-triferrocenyl-benzole.Die recht starren Konformationen der unsymm. Benzolderivate sowie des aus Acetylferrocen zugänglichen 1,3,5-Triferrocenyl-benzols lassen sich aus ihrenNMR- undUV-Spektren, sowie aus derORD des optisch aktiven Trimeren ableiten.Polycyclotrimerisierung von 1,1-Diacetylferrocen ergibt ein thermisch ziemlich stabiles, strukturell interessantes Polymeres.

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Cyclotrimerization of ferrocenyl acetylene and its derivatives under various conditions yields exclusively 1.2.4-triferrocenylbenzenes. Therefrom, the smooth trimerization upon purely thermal treatment of ferrocenyl- and methylferrocenyl-acetylenes seems especially remarkable. Optically active (-methylferrocenyl)-acetylene thereby affords a strongly active 1.2.4-tri-(-methylferrocenyl)-benzene. From ferrocenyl-methyl- and ferrocenyl-phenyl-acetylene, resp., employing Co₂(CO)₈ as a catalyst, sterically overcrowded (unsymmetrical) trimethyl- and triphenyl-triferrocenylbenzenes are obtained.The rather rigid conformations of the unsymmetrical benzene derivatives and of 1.3.5-triferrocenylbenzene (accessible from acetylferrocene) can be deduced from theirNMR- andUV-spectra, as well as from theORD of the optically active trimer.Polycyclotrimerization of 1.1-diacetylferrocene affords a thermically rather stable, structurally interesting polymer.

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Mit 3 Abbildungen

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Herrn Prof. Dr.J. W. Breitenbach zum 60. Geburtstag gewidmet.

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38. Mitt.:H. Falk undG. Haller, Mh. Chem.99, 279 (1968); die vorliegende Arbeit zählt unter dem Titel Cyclotrimerisierung von Ferrocenylacetylenen als 8. Mitt. über Ferrocen-Acetylene. 7. Mitt. s.G. Haller undK. Schlögl, Mh. Chem.98, 603 (1967).     

Aktivit?t und Selektivit?t der Palladiumkatalysatoren bei der Hydrierung isomerer n-Octine

Ohne Zusammenfassung     

A method for finding the roots of a polynomial

Summary Two variants of a method for finding the roots of a polynomial are described. A proof of the method for a general polynomial with complex coefficients is not based on neighbourhoods of saddle points which are sufficiently small. The speed of convergence is guaranteed since the method is a modification of the downhill method and since it can be used in combination with an arbitrary method which quickly converges in practice, but whose convergence cannot be proved.     

Comparison of four cholesterol‐based stationary phases for the separation of steroid hormones

The chromatographic behavior of steroid hormones on four cholesterol‐bonded stationary phases with different structures in binary methanol/water mobile phases was studied. Of the stationary phases tested, the commercially available stationary phases Cogent UDC cholesterol? and COSMOSIL cholester? provided better separations of steroid hormones in comparison to homemade aminocholesterol and diaminocholesterol stationary phases. The results show that the temperature has a significant influence on the retention and selectivity for steroid hormones separation. The temperature increase may cause changes in the elution order. From the dependences of the retention (ln k) on temperature (1/T), the standard partial molar enthalpy and standard partial molar entropy were calculated and their enthalpic and entropic contributions to the retention were compared. The enthalpic effects principally control the retention mechanism.