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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 97 (1993), S. 10394-10402 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 89 (1985), S. 5518-5521 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 6 (1974), S. 601-602 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbon-13 NMR chemical shifts have been measured in a number of binary mixtures of normal alkanes. Intrinsic solvent shifts are deduced from the shifts and the relevance of some small substituent effects in alkanes is discussed. A comparison is made between solvent effects and thermally induced chemical shift differences in alkanes.
    Additional Material: 3 Tab.
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  • 4
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Direct and long-range 13C—1H coupling constants are presented for the enone moieties of cyclopent-2-enone, cyclohex-2-enone and their protonated derivatives. A correlation is given between the experimental values and the results of quantum chemical calculations (CNDO/2, INDO). The existing calculations are modified in order to improve the relationship between the calculated and experimental results.
    Additional Material: 1 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 5 (1973), S. 147-153 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 13C NMR (CMR) spectra of a number of di- and trisubstituted ethylenes have been measured. Very consistent values are found for the differential shieldings of allylic carbons in a number of linear, (Z)- and (E)-disubstituted ethylenes. The discrepancies between the several structural elements are explained tentatively by assuming different rotational preferences in the (Z)-isomers, the (E)-isomers, or both. The results obtained for some branched olefins are qualitatively in agreement with conclusions reached in previous 1H NMR (PMR) investigations, with the possible exception of 2,5-diMe-3-hexene.Differential shieldings in trisubstituted ethylenes are larger than in disubstituted ethylenes, probably as a consequence of steric interaction between geminal substituents.It is confirmed, that API's recent relabelling of the isomers of 3-Me-2-hexene was justified. Furthermore, the (E)-configuration is assigned to the high-boiling isomer of 3,4,4-triMe-2-pentene. On the other hand, the high-boiling isomer of 3-Et-4-Me-2-pentene is shown to be the (Z)-isomer. For the isomeric pair of geraniol and nerol, the (E)-configuration is assigned to the former and the (Z)-configuration to the latter, in agreement with our recent PMR investigations.
    Additional Material: 6 Tab.
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  • 6
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 13C n.m.r. chemical shifts of a number of 1,1-disubstituted ethylenes are presented. Moreover, effects of changing temperatures on the 13C n.m.r. chemical shifts of some of these compounds as well as of three normal alkanes are given. These variations in chemical shifts are attributed to varying amounts of sterically induced shifts in the different conformational equilibria. In addition to the well-known 1,4 interaction between two alkyl groups shielding effects on the carbon atoms of the connecting bonds are also proposed. No definite explanation of this effect is presented at this time. It is further shown that no simple correlations exist between 13C n.m.r. chemical shifts and calculated total charge densities at this level. Instead, the experimental results in 1-alkenes are rationalized by assuming a linear dependence of the 13C n.m.r. chemical shifts of C-1 and C-2 via rehybridizations on changes in bond angles for small skeletal deformations caused by steric interactions. These changes in geometries, as well as conformational energies in three 1-alkenes, were calculated by means of VFF calculations. Finally. upfield shifts for both C-2 and C-4 are proposed for those conformations of 1-alkenes in which the C-3—C-4 group interacts with the pz-orbital of C-2.
    Additional Material: 4 Tab.
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 11 (1978), S. 316-318 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The γ-effects of sulphur on 13C NMR chemical shifts have been measured in a series of steroidal compounds containing the thiophene ring in different configurations with respect to the rest of the molecule. The data constitute the first example of downfield effects exerted by sulphur on both gauche and antiperiplanar γ-carbons. The γ-gauche effect of sulphur amounts to 1.6-1.8 ppm, the γ-antiperiplanar effect from practically zero to almost 1 ppm.
    Additional Material: 1 Tab.
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  • 8
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Capillary Gas Chromatography (CGC) is capable of determining underivatized cyclophosphamide (CPA) using SCOT OV 275 columns. Then CPA is subjected to in situ degradation resulting in formation of a cyclization product which can be determined selectively in biological fluids. In routine bioanalysis however cyclization products of CPA metabolites might interfere, e.g. 4-keto CPA. In the present study possible formation of cyclization products of 4-keto CPA similar to CPA was monitored by Mass Spectrometry. Cyclization of 4-keto CPA in situ was demonstrated to occur, resulting in a product similar to that of CPA. Both cyclization products could be determined selectively and it appeared that in situ cyclization of 4-keto CPA was negligible (〈5%), probably owing to extra stabilization of the CPA metabolite by keto-enol tautomerism as has been demonstrated by NMR.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0935-6304
    Keywords: Capillary GC ; RP-HPLC ; CP-MAS NMR ; Deactivation methods ; Hexamethyldisilazane ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of Cab-O-Sil, a highly dispersed vitreous quartz, with hexamethyldisilazane (HMDS) was studied in the temperature range 380-500°C, using 29Si solid state NMR and other techniques. Such studies are of importance in view of deactivation procedures of fused silica at high temperatures in capillary GC.The commonly accepted reaction equation: \documentclass{article}\pagestyle{empty}\begin{document}$$ \left({{\rm Me}_{\rm 3} {\rm Si}} \right)_2 {\rm NH } + {\rm 2}\equiv {\rm SiOH} \to {\rm 2} \equiv {\rm SiOSiMe}_{\rm 2} + {\rm NH}_{\rm 3} $$\end{document} predominates only below ca. 400°C. Above ca. 400°C the intermediate cleavage product Me3SiNH2 reacts with surface silanol groups to form ≡SioSiMe2NH2 + CH4. At higher temperatures these groups may ultimately form (≡SiO)3SiNH2 groups (analogously to the formation of bi-and tridentate linkages starting from ≡SiOSiMe3 groups), but (≡SiO)3SiNH2 groups are also directly formed at lower temperatures, simultaneously with the ≡SiOSiMe3 groups, probably by reaction with siloxane bridges: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm Me}_3 {\rm SiNH}_2 + \equiv {\rm SiOSi} \equiv\; \to \;\equiv SiNH_2 + \equiv SiOSiMe_3 $$\end{document}.The reactions of the trimethylsilylamine part of HMDS with Cab-O-Sil were confirmed by an independent series of silylations using N,N-dimethyltrimethylsilylamine instead of HDMS. The presence of amino groups as ≡SiNH2 was confirmed by FT-IR. This may be one of the reasons why very high temperature silylation with disilazanes does not provide a satisfactory deactivation of fused silica GC columns: the active ≡SiOH groups are “replaced” by active ≡SiNH2 groups. However, such a material may be of interest in LC. Silylation with silazanes at ca. 350°C in humid atmosphere and/or after extensive hydroxylation (leaching) of the surface should yield sufficiently deactivated surfaces with a rather well defined surface structure.
    Additional Material: 5 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 564 (1988), S. 72-80 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: A Method for the Identification of T-Atom Vacancies in the Lattices of ZeolitesSilanol groups in the lattices of zeolites can be silylated with trimethylchlorosilane and the products can be characterized by means of 29Si (CP) MAS NMR. T-atom vacancies are indicated by the formation of silylation products with three or four siloxy-linkages under mild reaction conditions as this requires the presence of three or silanol groups in favourable geometrical arrangements.
    Notes: Am Beispiel der Zeolithe ZSM-5 und Y wird gezeigt, wie amn Gitter-Leer-stellen in Zeolithen identifizieren kann. Terminale Hydroxylgruppen, die auch Gitter-Leerstellen umgeben, werden dabei mit Trimethylchlorsilan (TCS) silyliert und die Produkte mit 29Si-(CP)-MAS-NMR untersucht. Die Anwesenheit von Gitter-Leerstellen wird angezeigt durch die Bildung von Silylierungsprodukten mit drei oder vier Siloxybindungen, die Insertion des TCS zwischen drei beziehungsweise vier terminalen Hydroxylgruppen im Zeolithgitter unter sehr milden Reaktions bedingungen entstehen.
    Additional Material: 4 Ill.
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