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  • 1
    Electronic Resource
    Electronic Resource
    23Na nuclear magnetic resonance study of the complexation of sodium tetraphenylborate by [5,5]-dibenzo-30-crown-10 in nitromethane, acetonitrile, acetone and pyridine (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 435-442 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The nature of the (Na-DB30C10)+ complex has been studied by 23Na NMR in four non-aqueous solvents: nitromethane (NM), acetonitrile (AN), acetone (AC) and pyridine (PY). The equilibrium constant of formation (Kf) of (Na-DB30C10)+ in AC, AN and PY was determined at 300 K: log Kf = 3·9 ± 0·3, 3·4 ± 0·5 and 3·0 ± 0·1, respectively. In cases such as in pyridine, where exact values of the rate constants for the chemical exchange could not be calculated, limiting values were determined giving k-1 (the rate constant for complex dissociation) 〉 6·6 × 10-4 s-1 and kc (the rate constant for the formation of the complex) 〉 5 × 107 l mol-1 s-1. Evidence was found for the formation of a 2 : 1 (Na2-DB30C10)+2 complex in nitromethane. It has been previously shown that for (Na-DB24C8)+ the first coordination sphere of Na+ is exclusively filled by the oxygens of the crown ether, whereas for (Na-DB18C6)+ there is participation of at least one solvent molecule. The first coordination sphere of Na+ in (Na-DB30C10)+ consists of one or several molecules of solvent in addition to a number of oxygens from the crown ether. The soft wrapping of the Na+ by DB30C10 is in constrast with the hard wrapping of Na+ by DB24C8 and of K+ by DB30C10.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030704
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  • 2
    Electronic Resource
    Electronic Resource
    Preferential Solvation of the Sodium Cation in Binary Mixtures of Tetrahydrofuran with Polyamines, in Relation with the Chelate Effect (1981)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 556-567 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The problem of determining the chelate effect brushes against methodological snags: the choice of concentration units, and of the appropriate standard states. We avoid these pitfalls by defining the chelate effect from measurements on bidentate ligands alone, without recourse to comparison with the corresponding unidentate ligands. Quantitation of the parameters extracted from the data is effected by three independent and mutually consistent procedures. Solvation of the Na+-cation by the polyamines follows the sequence: cadaverin 〈 1, 3-diaminopropane ≪ ethylene diamine ≪ diethylenetriamine. Entry of the first and of the second diamine molecule into the sodium coordination shell are independent and equiprobable steps: K1 = K3 and K2 = K4, within the accuracy of the measurements. For ethylene diamine, the values of K1 and K3 are in the range 1.0-1.5 and those for K2 and K4 are in the range 83-102: attachment of the second N-atom is considerably easier, by two orders of magnitude (chelate effect). The chelate effect is strongly reduced in cadaverin, with a longer hydrocarbon chain connecting the two amine functions.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19810640219
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  • 3
    Electronic Resource
    Electronic Resource
    Coordinating Abilities Towards Sodium of Oxygenated Solvents (1976)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 59 (1976), S. 1333-1345 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetracoordination of the sodium cation is indicated by the 23Na-NMR. chemical shifts for NaClO4 in binary mixtures of ether and alcohol solvents. Solvent exchange occurs by a sequential process, and involves one or several intermediates. In competition with tetrahydrofurfuryl alcohol, whereas glyme corresponds to monocyclic intermediates, diglyme and triglymeFor abbreviations see Table 1. favor formation of bicyclic intermediates. The relevant conformational factors are analysed, and also serve to explain the better coordinating abilities of diglyme and triglyme, as compared to glyme. The mechanism for solvent exchange is discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19760590436
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  • 4
    Electronic Resource
    Electronic Resource
    23Na-NMR. Linewidths in Binary Mixtures of Oxygenated Solvents (1976)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 59 (1976), S. 1346-1351 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The inference of single bicyclic intermediates in the competition of diglyme (or triglyme)For abbreviations see the table of [1]. with tetrahydrofurfuryl alcohol is confirmed by analysis of the linewidths. The dissymetric bicyclic species are characterized by linewidths increased markedly with respect to the pure solvents, without an accompanying change in the 23Na chemical shift. Conversely, the competition of glyme with the same alcohol involves three equi-probable intermediates; that of tetrahydrofuran (or tetrahydropyran) is of greater conceptual complexity.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19760590437
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  • 5
    Electronic Resource
    Electronic Resource
    Influence of Amino Acids, Ammonium and Potassium Cations on the Self-Assembly of 5′-GMP (1979)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 62 (1979), S. 1559-1565 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-ordered supramolecular structures formed by 5′-guanosine monophosphate (disodium salt) in aqueous solution at pH 7.8 show pronounced interaction with ammonium ions. Rather than competing with potassium ions for the central cavity in hydrogen-bonded guanine tetramers, ammonium ions bring about - in synergism with potassium ions - further aggregation. Glycine appears to destroy the aggregates, by competing with potassium ions for the core positions within the tetramers. Conversely, alanine does not interact significantly with the system. These conclusions follow from analysis, at various concentrations, of the microdynamics and of the mole fractions of sodium ions bound to self-assembled 5′-GMP--, obtained from relaxation rate measurements for the 23Na nucleus, as the 5′-GMP-- counter-ion.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19790620521
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  • 6
    Electronic Resource
    Electronic Resource
    Preferential Solvation of the Sodium Cation in Binary Mixtures of Tetrahydrofuran with Unidentate Nitrogen Ligands (1981)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 547-555 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 23Na-chemical shifts for the NaClO4 solute depend markedly upon the composition of binary solvent mixtures of THF with amines (pyridine, piperidine, pyrrolidine, aniline, propylamine, and isopropylamine). These changes, analyzed in a novel application of the Hill formalism, show equality of the intrinsic equilibrium constant K for the successive steps, upon displacement of THF from sodium coordination by one of these amines. The results, which are entirely consistent with tetracoordination of the sodium cation by these solvents, also indicate proportionality of the K values to the amine chemical shifts.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19810640218
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