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  • Chemistry  (84)
  • 550 - Earth sciences  (26)
  • Life and Medical Sciences  (2)
  • 1995-1999  (64)
  • 1985-1989  (48)
  • 1
    Electronic Resource
    Electronic Resource
    Two-component diacrylate networks from liquid-crystalline and non-liquid-crystalline monomers I. Synthesis of the monomers, phase behaviour of the binary monomer mixtures, network formation (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 250 (1997), S. 105-117 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Aus Bisacrylaten wurden durch photoinduzierte Vernetzung in der isotropen Phase zweikomponentige Netzwerke synthetisiert. Bei allen Systemen wurde als eine Komponente ein Bisacrylat verwendet, das eine flüssigkristalline Phase bilden kann, und als zweite Komponente ein Bisacrylat, das dazu nicht in der Lage ist. Die isotrope Komponente wurde hinsichtlich ihrer Größe, Geometrie und Polarität variiert. Für alle Systeme wurden mittels einer Wärmeflußkalorimetrie (DSC) Phasendiagramme der Monomermischungen erstellt. Das Phasenverhalten der Systeme zeigt eine Abhängigkeit vom Schmelzpunkt und der chemischen Struktur der isotropen Zweitkomponente. Die Vernetzungstemperatur wurde so gewählt, dafß die Vernetzung in der isotropen Phase 10 °C über der Phasenllbergangstemperatur erfolgte. Die Reaktionskinetik wurde aus den Photopolymerisationsenthalpien mittels eines für photochemische Vernetzungen modifizierten DSC-Gerätes untersucht. Die Zeitabhängigkeit des Umsatzes und der Gesamtumsatz an Acrylatbindungen wurden aus den DSC-Kurven ermittelt. Der Gesamtumsatz hängt nicht von der Reaktionstemperatur und der Struktur der Monomeren ab und liegt je nach Zusammensetzung füralle Systeme zwischen 53 und 71%. Die Zeitabhängigkeit des Umsatzes hingegen wird von der Struktur des nicht flüssigkristallinen Comonomeren beeinflufßt.
    Notes: Two-component networks of diacrylate monomers were synthesized by photoinduced polymerization in the isotropic phase. In all systems one component was a liquid-crystalline diacrylate, whereas the second component was a non-liquid-crystalline diacrylate, which was varied in size, geometry and polarity. The phase behaviour of the monomer mixtures has been analysed by differential scanning calorimetry (DSC). It is influenced by the melting point and the structure of the non-liquid-crystalline component. All samples were cross-linked in the isotropic phase 10°C above the phase transition temperature and a modified differential scanning calorimeter was used to investigate the enthalpies of photopolymerization. The final value and the time dependence of the conversion of acrylate double bonds were calculated from the DSC curves. The final degree of conversion of the acrylate double bonds was between 53 and 71% for all samples, whereas no significant dependence of the degree of conversion on the chemical structure of the monomers or the reaction temperature has been found. In contrast, the time dependence of the conversion was influenced by the chemical structure of the non-liquid-crystalline component.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052500108
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  • 2
    Electronic Resource
    Electronic Resource
    Versuche zur Synthese von Calicen aus trisubstituierten Cyclopropanen und Cyclopentenon56. Mitt. über Fulvene, Fulvalene; 55. Mitt. [1]: Kurzmitt. (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 41-50 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Attempted Synthesis of Calicene from Trisubstitued Cyclopropanes and CyclopentenoneThe Li carbenoids 4, prepared by treatment of substituted 1,1-dihalocyclopropanes with BuLi, are reacted with cyclopent-2-enone under thermodynamic and kinetic control (Scheme 1). In general, the latter procedure gives better yields of cyclopropylcyclopentenols 5a-e, but the reaction seems to be controlled mainly by the steric and electronic properties of the substituent Y. So, with 4b and 4e, the main reaction is the attack of the carbenoid at C(1) of cyclopent-2-enone, while 4a (Y = PhS) predominantly deprotonates the ketone (Scheme 4). Whereas 5d and 5e can easily be converted to the dihydrocalicenes 6d and 6e (Scheme 6), the attempted elimination of H2O from 5a-c leads to the rearranged products 13-2 due to the opening of the cyclopropane ring (Scheme 5). Finally, the generation of the parent compound 2 from the silylated precursor 6d is attempted: treatment with MeO- gives the addition products 18A/18B, while the reaction with Br2 provides 19 by a bromination/dehydrobromination sequence (Scheme 7).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19890720106
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  • 3
    Electronic Resource
    Electronic Resource
    8-Substituted Xanthines as Phosphodiesterase Inhibitors: Conformation-Dependent Lipophilicity and Structure-Activity RelationshipsPresented in preliminary from at the 7th European Symposium on Quantitative Structure-Activity Relationships, Interlaken, September, 1998. (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 507-517 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 8-substituted xanthines 1-21 (including compound S 9795), caffeine (22), and the three isomeric dimethyl-xanthines 23-25 (see Table 1), were examined for their lipophilic behaviour using a reversed-phase HPLC technique. A number of flexible compounds showed a smaller-than-expected lipophilicity which based on conformational and tautomeric calculations were ascribed to the predominance of folded forms. A QSAR analysis of the phosphodiesterase-inhibitory potency of several compounds showed favourable factors to be a low lipophilicity and the absence of a substituent on the N7 position.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19890720314
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  • 4
    Electronic Resource
    Electronic Resource
    Dimere Phospha- und Thiastannylene: Ylidartige Diphospha- und Dithiadistannetane (1985)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 118 (1985), S. 1045-1049 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Dimeric Phospha- and Thiastannylenes: Ylide-type Diphospha- and DithiadistannetanesBis(di-tert-butylphosphino)tin(II) (1) is obtained from the reaction of potassium di-tert-butyl-phosphide with stannous chloride or with the stannous chloride-triethylphosphane complex. Bis(tert-butylthio)tin(II) (2) is prepared by reaction of (η5-C5H5)2Sn with 2-methyl-2-propanethiol or from stannous chloride and (tert-butylthio)trimethylsilane. In solution, 1 and 2 are PR2-and SR-bridged dimers, respectively. NMR spectra indicate that rapid scrambling of terminal and bridging substituents occurs in 2 but not in the cyclic \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm P}\limits^ + - \mathop {\rm S}\limits^{\rm - } {\rm n} $\end{document} ylide 1.
    Notes: Bis(di-tert-butylphosphino)zinn(II) (1) entsteht durch Reaktion von Kalium-di-tert-butylphos-phid mit Zinndichlorid oder dem Zinndichlorid-Triethylphosphan-Komplex. Bis(tert-butylthio)-zinn(II) (2) wird hergestellt durch Umsetzung von (η5-C5H5)2Sn mit 2-Methyl-2-propanthiol und entsteht auch bei der Reaktion von Zinndichlorid mit (tert-Butylthio)trimethylsilan. 1 und 2 liegen in Lösung als PR2- bzw. SR-verbrückte Dimere vor. Kernresonanzspektren zeigen, daß bei dem cyclischen \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm P}\limits^ + - \mathop {\rm S}\limits^{\rm - } {\rm n} $\end{document}-Ylid 1 im Gegensatz zu 2 auch in Ethern keine raschen Platzwechselvorgänge (Brücke/terminal) ablaufen.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19851180321
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  • 5
    Electronic Resource
    Electronic Resource
    Eigenschaften von Tellur-Tellur-Bindungen, VI. Struktur und Barriere der Enantiomerenumwandlung von Bis(2,4,6-tri-tert-butylphenyl)ditellan (1988)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 121 (1988), S. 11-14 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Properties of Tellurium-Tellurium Bonds, VI.  -  Structure and Barrier of Interconversion of Enantiomeric Conformations of Bis(2,4,6-tri-tert-butylphenyl)ditellaneOxidation of lithium (2,4,6-tri-tert-butylphenyl)telluride provides red and strong refractive needles of bis(2,4,6-tri-tert-butylphenyl)-ditellane (1) which crystallize monoclinically in the space group C2/c. The bond distance d(Te-Te), the bond angle at the Te atoms, and the torsion angle at the Te-Te bond were found to be 271.3 pm, 100.6°, and 92.1°, respectively. The C2 symmetry of the molecule gives rise to different chemical surroundings for both tert-butyl groups in ortho position belonging to the aryl groups. This effect can also be observed in solution at low temperatures. For the first time, dynamic NMR spectroscopy succeeded in determination of the barrier of rotation about a Te-Te bond. This barrier was found to be 40.9 kJ · mol-1 and is 20% less than that in the corresponding diselane.
    Notes: Bis(2,4,6-tri-tert-butylphenyl)ditellan (1) wird durch Oxidation von Lithium-(2,4,6-tri-tert-butylphenyl)tellurid in Form roter, stark lichtbrechender Kristalle erhalten. 1 kristallisiert monoklin in der Raumgruppe C2/c. Der Bindungsabstand d(Te-Te) beträgt 271.3 pm, der Bindungswinkel an den Te-Atomen 100.6° und der Torsionswinkel an der Te-Te-Bindung 92.1°. Durch die C2-Symmetrie besitzen die beiden ortho-ständigen tert-Butylgruppen der Substituenten unterschiedliche chemische Umgebung, die auch in Lösung bei tiefen Temperaturen erkennbar wird. Aus NMR-spektroskopischen Daten gelang erstmals die Bestimmung der Rotationsbarriere um eine Te-Te-Bindung; sie beträgt 40.9 kJ · mol-1. Dieser Wert ist um 20% kleiner als für das entsprechende Diselan.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19881210103
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  • 6
    Electronic Resource
    Electronic Resource
    Eigenschaften von Chalkogen-Chalkogen-Bindungen, XI. Iod[tris(trimethylsilyl)methyl]selan: Synthese des ersten Alkylselenenyliodids (1988)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 121 (1988), S. 2109-2110 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Iodo[tris(trimethylsily)methyl]selane: Synthesis of the First Alkylselenenyl IodideBis[tris(trimethylsilyl)methyl]diselane (1) reacts with elemental iodine to provide iodo[tris(trimethylsilyl)methyl]selane (2) in high yield. 2 is the first iodoselane that does not suffer from redismutation equilibria in solution at ambient temperature with iodine and the parent diselane.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19881211206
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  • 7
    Electronic Resource
    Electronic Resource
    Reactions at Silicon-Silicon Bonds, V. Selective Trichlorosilylation of Alkyl(diorganylamino)chlorophosphanes with Hexachlorodisilane or with Trichlorosilane/Triethylamine. - Two Routes to New Functional Trichlorosilylphosphanes (1995)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 128 (1995), S. 615-619 
    Details
    ISSN: 0009-2940
    Keywords: Reductive silylation ; Aminochlorophosphanes ; Silylphosphanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of alkyl(diorganylamino)chlorophosphanes R(R2′N)PCl 1 (1a: R = tBu, R′ = Et, 1b: R = iPr, R′ = iPr; 1c: R = iPr, R′ = Ph) with hexachlorodisilane, afforded alkyl(diorganylamino)trichlorosilylphosphanes R(R2′N)PSiCl3 2 (2a: R = tBu, R′ = Et; 2b: R = iPr, R′ = iPr; 2c: R = iPr, R′ = Ph) and silicon tetrachloride. An intermediate formed in the reaction of 1b with hexachlorodisilane, the adduct iPr(iPr2N)(Cl)P-Si(Cl)3-SiCl3 (3b = 1b · Si2Cl6), was detected by 31P- and 29Si-NMR spectra that indicate pentacoordinated silicon bound to tetracoordinated phosphorus and tetracoordinated silicon. Trichlorosilylphosphanes 2 are also available from 1 under very mild conditions by reductive trichlorosilylation with trichlorosilane in the presence of triethylamine. Compounds 2 were identified analytically, by mass spectroscopy, multinuclear NMR, and an X-ray structure determination of 2c.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19951280614
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis, Structure and Reactions of the Homoleptic Alkyne Nickel(0) Complex (Alkyne)4Ni3 (Alkyne: 2-methyl-4-trimethylsilyl-3-butyn-2-ol)Dedicated to Professor Walter Siebert on the occasion of his 60th birthday. (1996)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 129 (1996), S. 1457-1461 
    Details
    ISSN: 0009-2940
    Keywords: Nickel(0) ; Alkyne complexes ; Hydrogen bonds ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of (cdt)Ni (cdt: cyclododeca-1,5,9-triene) with 2 equivalents of 2-methyl-4-trimethylsilyl-3-butyn-2-ol leads to the selective formation of the homoleptic complex (alkyne)4Ni3 (compound 3), which can be isolated in excellent yields. The solid-state structure of 3 exhibits three Ni centers, forming a bent Ni3 chain connected by two bridging alkynes. The other two alkynes are terminally coordinated. Additionally, the trimeric units are stabilized by three intramolecular hydrogen bonds. Two intermolecular hydrogen bonds connect the trimeric units to form a polymer rope. According to the 13C- and 1H-NMR spectra in THF the structure of the complex 3 in solution is very similar to that in the solid state. The reaction of 3 with some alkynediols and with 2,5,5-trimethylhex-3-yn-2-ol affords compounds of the type (alkyne)2Ni. Cot (cot: 1,3,5,7-cyclooctatetraene) converts 3 into [(cot)Ni]2, which in turn reacts with 2,5-dimethylhex-3-yne-2,5-diol to form the dimeric complex (alkyne)2Ni2(cot) 6. X-ray analysis of 6 reveals a very symmetrical structure in which cot connects both Ni(0) centers at opposite sides of the ring system.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19961291210
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  • 9
    Electronic Resource
    Electronic Resource
    Reactions of Silicon-Silicon Bonds, VIFor part V, see ref.[1].. Reductive Trichloroslilylation Reactions Leading to Alkyl- and Dialkylaminobis(trichlorosilyl)phosphanesDedicated to Professor Walter Siebert on the occasion of his 60th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 377-384 
    Details
    ISSN: 0009-2940
    Keywords: Trichlorosilylation ; Dichlorophosphanes ; Silylphosphanes ; Amino(silyl)phosphanes ; Silicon /Reductions ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of hexachlorodisilane and of trichlorosilane/triethylamine with alkyl-and dialkylaminodichlorophosphanes RPCl2 1a-i [R = iPr: a; (Me3Si)2CH: b; R=1-adamantly: c: R=tBu: d; R=Et2N: e; R=iPr2M: f] furnish bis(trichlorosilyl)-phosphanes RP(SiCl3)2 3a-f. However, when less bulky substituents are attached to the phosphorus atom, so that there is little steric crowding, the double reductive silylations leading from 1 to 3 are accompanied by side reactions and decomposition of 3. Therefore, only 3b, 3c, 3d, and 3f wre isolated in a pure state. These compounds are more readily prepared by the; trichlorosilane/triethylamine method. 1H-, 31P- and 29Si-Nmr spectra confirm their constitution. The structure of solid 3f, the first aminobis(trichlorosilyl)phosphane, was determined by X-ray crystallography. 3f contains a phosphorus atom in a pyramidal environment surrounded by two silicon atoms and a planar nitrogen atom of the diisopropylamino group.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300312
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  • 10
    Electronic Resource
    Electronic Resource
    Reversible Rearrangements of Chlorophosphane-Dichlorogermylene Ylides to Trichlorogermylphosphanes  -  Structure Determination of a Tetranuclear Bis(chlorophosphane)bis(trichlorogermylphosphane) Silver Bromide Complex (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1619-1623 
    Details
    ISSN: 0009-2940
    Keywords: Dichlorogermylene ; Trichlorogermylphosphanes ; Insertion ; Silver bromide complex ; Carbene homologues ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chlorophosphanes RR'PCl (1a: R,R' = 1b: R = tBu, R' = iPr, 1c: R = iPr, R' = Et2N, 1d: R = Et2N react with the dichlorogermylene dioxane complex 2 furnishing trichlorogermylphosphanes RR'PGeCl3 4a-d. In the cases of 1c/4c and 1d/4d the insertion reaction remain incomplete; similarly, 4a always contains, shortly after isolation in pure state, small amounts of 1a that can be detected by NMR. A provided by the reaction of trichlorosilylphosphane tBu(Et2N)PSiCl3 (5d) with GeCl4. The alkyl(dialkylamino) trichlorogermylphosphane 4d exists only in an equilibrium with chlorophosphane 1d, which coordinates GeCl2 leading to the dichlorogermylene complex 3d. A 1:1 mixture of 4a with 1a is formed by the novel cleavage (“chlorogermylation”) of the P-P bond of tetraisopropyldiphosphane with germanium tetrachloride. Di-tert-butyl(trichlorogermyl)phosphane 4e (R, R' = tBu) reacts with silver bromide providing a crystalline silver complex 7. A structure determination by X-ray diffraction reveals that 7 is [Ag4Br4(tBu2PCl)2(tBu2PGeCl3)2]. 2C7H8. Two of the Ag atoms of the cubane-like (AgBr)4 core of 7 are coordinated by chlorophosphane 1e, the other two by trichlorogermylphosphane 4e.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971301110
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