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  • 1
    Electronic Resource
    Electronic Resource
    119Sn spin-lattice relaxation times and nuclear Overhauser enhancement factors in some organotin compounds (1982)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 20 (1982), S. 170-174 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dipole-dipole relaxation via non-bonded protons is an important relaxation mechanism for119Sn in tri-n-propyltin and tri-n -butyltin compounds. This causes a negative nuclear Overhauser effect, arising from the negative magnetogyric ratio, which in some cases nulls the signal. The relative contributions from the spin-rotation and dipole-dipole mechanisms vary: larger molecules have lower spin-rotation and higher dipolar relaxation rates. The practical significance of large nuclear Overhauser enhancement factors in recording 119Sn spectra and the relation of the dipole-dipole contribution to the molecular motion and of the spin-rotation contribution to the absolute shift scale for 119Sn are discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270200312
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  • 2
    Electronic Resource
    Electronic Resource
    Use of high-field 119Sn NMR and the pairwise additivity model for chemical shifts in the identification of complexes in the SnBr4-KSCN-MeOH system (1986)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 24 (1986), S. 921-926 
    Details
    ISSN: 0749-1581
    Keywords: 119Sn NMR ; Pairwise additivity model ; Inorganic tin(IV) complexes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of SnBr4 and KSCN in methanol solution has been studied by 119Sn NMR at 149 MHz and -30°C. Evidence was obtained for the existence of both the cis and trans isomeric forms of SnBr4·2MeOH. A pairwise additivity model for chemical shifts was used to explain the observed peaks and many of the possible species, SnBrn(NCS)4-n·2MeOH. [SnBrn(NCS)5-n·MeOH]- and [SnBrn(NCS)6-n2-], (n=0-4), and their somecies, forms were identified and shown to exist simultaneously in solution in complex equilibria. In some cases 119Sn-14N coupling was observed. The implications for possible synthesis of these types of compounds and the necessity for measurement at high field are discussed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260241016
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  • 3
    Electronic Resource
    Electronic Resource
    ESR spectroscopic investigation of some 4-substituted 1,3,2-dithiazolyl and 2,3,1-dithiazolyl radicals (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 666-672 
    Details
    ISSN: 0749-1581
    Keywords: Electron spin resonance spectroscopy ; Sulphur-nitrogen-containing radicals ; Dithiadiazolyl radicals ; Dithiadiazolyl radicals ; Dithiazophospholyl radicals ; Phosphaalkynes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Further information has been obtained on the electronic structure of 1,3,2-dithiazol-2-yl radicals. The structure has been well characterized previously except for positions 4 and 5 in the ring. We have obtained solution and powder ESR spectra of radicals substituted with 13C in both positions and of radicals substituted with nitrogen or phosphorus in the 4-position. It is probably the first time that a compound has been prepared containing the ring. Two especially interesting facts emerged from the ESR spectra of these 1,3,2-dithiazolyl radicals: the 13C-substituted radical has a considerable amount of p spin density in the plane of the ring and the phosphorussubstituted radical has a very low unpaired spin density at the phosphorus atom. It is known that 1,3,2,4-dithiadiazolyl radicals isomerize readily by photolysis to the symmetrical 2,3,1,4-dithiadiazolyl radicals; we attempted the same reaction with But and a new radical was produced that we have been unable to identify.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260300717
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  • 4
    Electronic Resource
    Electronic Resource
    NMR relaxation and ESR spin probe studies of some surfactant micelles (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 1000-1011 
    Details
    ISSN: 0749-1581
    Keywords: NMR relaxation ; Carbon-13 ; Deuterium ; ESR ; Micelles ; Surfactants ; Spin probes ; Alkyl chains ; Molecular dynamics ; ‘Two-step’ model ; ‘Three-step’ model ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multi-frequency relaxation studies combined with the ‘two-step’ and ‘three-step’ models for molecular motion have been applied to a range of anionic surfactant molecules. From the internal dynamic parameters (τf and S) conclusions have been drawn about the dependence of surfactant molecular dynamics inside micelles on molecular structure, and two unusual conformations have been identified. Slow correlation time (τs) data have also been obtained for these compounds. Three deuteriated surfactant molecules were subjected to the ‘three-step’ model and data are presented showing how the dimensions of the non-spherical micelles vary with temperature. An ESR spin probe study has been carried out on the compounds giving probe rotational correlation times at various temperatures. Information on alkyl chain packing at or near the water/micelle interface can be obtained from the derived thermodynamic parameters.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260301016
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  • 5
    Electronic Resource
    Electronic Resource
    Carbon-13 NMR relaxation studies of some dicyclohexyl compounds (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 777-785 
    Details
    ISSN: 0749-1581
    Keywords: Carbon-13 relaxation ; Molecular motion ; Rotational barriers ; Dicyclohexyl compounds ; Traction fluids ; Molecular modelling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four dicyclohexyl compounds were studied, one of which is a traction fluid and the remainder have related structures in which the cyclohexane rings are separated by two or three carbon atoms. Carbon-13 NMR T1 and NOE data were obtained for the four compounds at 22.50 and 100.62 MHz over a wide temperature range. The data were fitted simultaneously to either a reduced Lorentzian spectral density or to a ‘model-free’ two-correlation time spectral density. For the first time it has been possible to observe the tracking from the full ‘model-free’ two-correlation time spectral density to the reduced Lorentzian spectral density. From the correlation times and activation energies derived from these fittings, it can be concluded that all the compounds have semi-rigid structures. Computer modelling of the structures and molecular mechanics calculations of the rotational barriers gave results in agreement with those from the NMR data. Similarly, it was found that the friction coefficients of the compounds correlate with the NMR and molecular mechanics conclusions, namely that the increased rigidity produced by the introduction of methyl groups into the linkage between the cyclohexane rings leads to a more effective traction fluids. Hence it seems to be feasible to design new traction fluids in the laboratory.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260290807
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  • 6
    Electronic Resource
    Electronic Resource
    Carbon-13 NMR relaxation studies of some dicyclohexyl compounds at high pressure (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 823-829 
    Details
    ISSN: 0749-1581
    Keywords: Dicyclohexyl derivatives ; 13C spin-lattice relaxation times ; High-pressure NMR ; Rotational-translational coupling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four dicyclohexyl compounds were investigated, one of which is a traction fluid and the remainder have related structures in which the cyclohexyl rings are separated by two or three carbon atoms. Carbon-13 spin-lattice relaxation times have been measured at 25.16 MHz at pressures up to 200 MPa over the temperature range 280-329 K. High-pressure relaxation data have been successfully interpreted in terms of the ‘model-free’ approximation. A pressure-dependent rotational coupling parameter, κ, was evaluated from a modified Stokes-Einstein-Debye relationship using experimentally determined pressure-dependent rotational correlation times. The smallest value of κ was found to be associated with the most rigid and least-extended molecule, showing that molecular shape has a significant effect on the rotational-translational coupling. The values obtained for the activation volumes derived from methyl group data suggest that barriers to internal motion are governed by intramolecular effects. It has been demonstrated that high-pressure 13C relaxation measurements can provide a powerful means of studying the relationship between molecular rigidity and the macroscopic behaviour of functional fluids.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260290813
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  • 7
    Electronic Resource
    Electronic Resource
    Comparison of the Woessner and the ‘model-free’ approaches for the analysis of carbon-13 spin-lattice relaxation data for methyl groups (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 259-262 
    Details
    ISSN: 0749-1581
    Keywords: Carbon-13 relaxation times ; NOE factors ; Methyl groups ; Dicyclohexyl compounds ; Alkyl chains ; Model lubricants ; Molecular dynamics ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbon-13 NMR relaxation data obtained for methyl groups in two dicyclohexane compounds were used to compare the Woessner and ‘model-free’ approaches. It is shown that the extra flexibility offered by the latter leads to a more successful analysis of the data.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260300312
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  • 8
    Electronic Resource
    Electronic Resource
    ESR spectroscopy of some dicyano-, pyrazino- and quinoxalino-1,3,2-dithiazolyl radicals (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 774-778 
    Details
    ISSN: 0749-1581
    Keywords: ESR ; 1,3,2-Dithiazol-2-yl radicals ; Pyrazine ; Quinoxaline ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several symmetrical 1,3,2-dithiazol-2-yl radicals have been examined that have in common nitrogen-containing substituents at the 4- and 5-positions, namely 4,5-dicyano-1,3,2-dithiazol-2-yl, [15N2]-1,3,2-dithiazolo [4,5-b] pyrazin-2-yl and 1,3,2-dithiazoleo [4,5-b] quinoxalin-2-yl. The ESR spectrum of the 4,5-dicyano radical does not reveal any 14N splittings from the cyanide groups; however, the pyrazine and the quinoxaline derivatives do have multi-lined well resolved spectra arising from substantial hyperfine interactions with these nuclei. The interactions are sufficiently large to be observed in the powder spectra of the latter. The presence of proton hyperfine interactions shows that unpaired-electron spin density is delocalized over all the rings. It has been found that the radicals attached to pyrazine and quinoxaline can be incorporated into single crystals of naphthalene and phenazine, respectively.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260300814
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  • 9
    Electronic Resource
    Electronic Resource
    Carbon-13 NMR relaxation study of the overall and internal motions in compounds containing n-octyl chains (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 273-281 
    Details
    ISSN: 0749-1581
    Keywords: Molecular motion ; Carbon-13 relaxation ; Octyl chains ; Polydecene ; Model lubricants ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C nuclear relaxation behaviour of n-alkyl chains in a variety of compounds can be described in terms of two relaxation times, one for tumbling (τc) and one for each carbon nucleus for the internal motions (τc). Relaxation data for the quaternary carbon nuclei of n-octylbenzene and n-octyl cyanide have been used to determine τc) and their activation energies [Ea(τc)]. These values have enabled τe and their associated activation energies [Ea(τe)] to be calculated for each carbon in the alkyl chains of the two compounds. In these compounds the values for C-6 appear to be invariant with τe(298) = 15 ± 2 ps and Ea(τc) = 15 ± 1 kJ mol-1. Assuming that these are universal values for all n-octyl chains, we have used them to calculate τe and Ea(τe) for other simple n-octyl compounds, thus allowing τc and E.a(τc) to be determined. It was found that Ea(τc) values correlate well with those for Ea(n/T) obtained from viscosity measurements. Di-n-octyl ether shows motional properties similar to those of the straightchain compounds.Simultaneous fitting of relaxation rate and NOE enhancement data measured over a range of radiofrequencies and temperatures permits a wealth of motional properties to be discerned when there is a suitable frequency dispersion. Both tri-n-octylamine and polydecene tumble sufficiently slowly to allow both relaxation rate and NOE data to be used to evaluate τc and τe and their activation energies without making any assumptions about C-6. The values of τc(298) and Ea(τc) obtained from C-6 for tri-n-octylamine are 314 ± 12 ps and 18.5 ± 0.4 kJ mol-1, respectively, and the corresponding values for polydecene are 576 ± 41 ps and 16.1 ± 1.3 kJ mol-1, respectively.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260290314
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  • 10
    Electronic Resource
    Electronic Resource
    ESR measurement of translational diffusion constants (1995)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 33 (1995), S. S107 
    Details
    ISSN: 0749-1581
    Keywords: diffusion constants ; cavity sampling function ; convolution fitting ; spin probes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ESR spectroscopy can be used to measure the translational diffusion constants of spin probes in a variety of media using a capillary method. Following preliminary work, it has been possible to improve upon the accuracy of determining diffusion constants in two ways. Both methods require an experimental measurement of the resonant cavity sampling profile. In the first procedure, this cavity profile is convolved with a trial Gaussian distribution and the result is compared with the experimental data obtained from the ESR measurements; the diffusion constant is then determined by graphical optimization. The second method is a graphical one based on a knowledge of the experimental diffusion profile and the cavity sampling profile. Both methods have been shown to give similar results but the second less rigorous corrected-zero method is generally simpler to apply. For a medium such as water, it takes several days to acquire the necessary experimental data but the time taken to carry out the experiment can be shortened (or slower rates of diffusion can be measured) by using a shielded resonant cavity.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260331317
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