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  • General Chemistry  (1,028)
  • Physical Chemistry  (232)
  • Wiley-Blackwell  (1,260)
  • Blackwell Publishing Ltd
  • 1990-1994  (1,260)
  • 1925-1929
  • 1990  (1,260)
Collection
Keywords
Publisher
  • Wiley-Blackwell  (1,260)
  • Blackwell Publishing Ltd
Years
  • 1990-1994  (1,260)
  • 1925-1929
Year
  • 1
    Electronic Resource
    Electronic Resource
    Structure and stability of 2σ/1σ* three-electron-bonded radical cations from 1,n-bis(alkylthio)alkanes in aqueous solutions (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 17-22 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A large number of 1,n-bis(alkylthio)alkanes, R′S(CH2)nSR″, was investigated by pulse radiolysis in aqueous solutions. The sulphur-centred radical cations, which were obtained on oxidation of the dithia compounds by ·OH radicals, are stabilized via 2σ/1σ* three-electron interaction between two sulphur atoms. Intramolecular stabilization is the only process observed for n = 2-4, whereas for longer chain compounds with n 〉 4 some intermolecular sulphur-sulphur interaction is also indicated. The stability and yields of the three-electron-bonded species also depend on the nature of the substituents R′ and R″, and for the intermolecular systems are a function of solute concentration. The results corroborate earlier investigations and demonstrate, in particular, that the optical parameters are a very sensitive measure of changes in electron density and structure of the three-electron-bonded systems.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030105
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  • 2
    Electronic Resource
    Electronic Resource
    Solvolysis of highly reactive phosphorus-sulphonic anhydrides. Stereochemical and chemical arguments for phosphathiacylium cation formation (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 23-34 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The stereochemistry and mechanism of solvolysis of optically active tert-butylphenylphosphinothioic-O-trifluoromethanesulphonate (1) in solvents of different ionizing power were studied. It was found that in solvents of high ionizing power and low nucleophilicity 1 ionizes with the formation of a phosphathiacylium cation (2) as the reaction intermediate. Product resulting from the reaction of 2 with anisole was isolated and characterized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030106
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  • 3
    Electronic Resource
    Electronic Resource
    Stereochemistry of silver-ion-assisted solvolysis of tert-butylphenylphosphinothioic iodidate. Phosphathiacylium cation formation (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 35-37 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Studies on the stereochemistry of silver-ion-assisted solvolysis of a new optically active tert-butylphenylphosphinothioic iodidate demonstrated that the reaction proceeds with inversion of configuration at the phosphorus atom. Evidence for phosphathiacylium cation formation as a reactive intermediate is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030107
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  • 4
    Electronic Resource
    Electronic Resource
    Probing of transient photoenol formation from ortho-methyl-substituted phenyl ketones by hydrogen-tritium exchange (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 38-40 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Studies on the photochemically induced hydrogen-tritium exchange in o-methyl-substituted phenyl ketones are reported. It is shown that the tritium exchange can be beneficial for probing transient photoenol formation, particularly when photochemical side-reactions are occurring.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030108
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  • 5
    Electronic Resource
    Electronic Resource
    Studies on organophosphorus compounds. XXXVI.For Part XXXV, see S. S. Li, Z. Y. Chen and C. Y. Yuan Scientia Sinica (Series B) 136, (1989).. Substituent effects of alkylphosphonates and -phosphinates in alkaline hydrolysis (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 48-54 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Alkaline hydrolysis of diethyl alkylphosphonates and alkyl diethylphosphinates was studied in aqueous dimethyl sulphoxide. The behaviour of these acyclic phosphorus esters is very similar to that of some cyclic phosphorus esters. Rate constants were measured at three temperatures over a 30°C range, and the activation functions of the reaction were estimated. The basic hydrolytic process was proved to be a bimolecular AE reaction. Multiple regression analyses involving rate constants and substituent parameters gave, as a rule, poor results using steric constants derived from carbon compounds. However, the substituent steric effect on the rate of hydrolysis of phosphonates and phosphinates studied correlated very well with ΔΔE, representing the difference in steric energy calculated by molecular mechanics. It is attributed to the various degrees of susceptibility of carbon and phosphorus atoms to the steric hindrance of the substituents. Moreover, Newman's rule of six for the hydrolytic reaction of carboxylates was completely eliminated in phosphorus ester hydrolysis.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030110
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  • 6
    Electronic Resource
    Electronic Resource
    The kinetic deuterium isotope effect of proton-transfer reactions in solution. Comparison of the marcus and the quantum-statistical mechanical models (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 62-68 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The free energy dependence of the kinetic deuterium isotope effect of proton-transfer reactions in solution is usually analysed in terms of the Marcus model. By means of modern computer techniques, the more general quantumstatistical mechanical model is also amenable to routine application. The differnces in the basic assumptions of the two approaches concerning the kinetic isotope effect are discussed. Reaction series for which both the Brønsted relation and the free-energy dependence of the kinetic isotope effect are available are analysed by means of the two models using one set of parameters for both free-energy relations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030112
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  • 7
    Electronic Resource
    Electronic Resource
    Porphyrin-tyrosine interactions: Photo-CIDNP and NMR studies (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 69-76 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Strong 1H and 13C nuclear polarizations are observed when aqueous solutions of synthetic water-soluble porphyrins are irradiated in the presence of tyrosine and some of its derivatives. These polarizations are strongly pH dependent. Evidence is also shown for the formation, in the dark, of a complex between the reactants. The association constants are evaluated from the NMR chemical shifts on the aromatic tyrosine protons induced by the presence of the porphyrins. The nature of the intermediate radical pair generating the CIDNP effects is discussed. An electron-transfer reaction from tyrosine to the excited triplet state of the porphyrin, or within the porphyrin-tyrosine excited complex, is expected to be the primary step in the reaction. It is followed by subsequent proton transfer within the initial ion radical pair. The spin polarizations arise principally from the back-transfer step, as the reactants are the only products which are polarized.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030202
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  • 8
    Electronic Resource
    Electronic Resource
    Brønsted coefficients and the theory of acid-base catalysis of proton transfers from carbon acids (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 95-109 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The intersecting-state model previously used to interpret proton transfers in ground and excited states and enzyme catalysis was applied to the general acid-base catalysis of carbon acids. The results are consistent with the predictions published for these systems and provide a new physical meaning for the Brønsted coefficients. It is shown that in addition to the linear free energy effect, the Brønsted coefficients are also influenced by the tightness of the transition states and by electronic effects. The model suggests that the increased reactivity of carbon acids towards proton transfer in non-hydrogen-bonding solvents is caused by an added electronic effect on the thermodynamics of the reactions. The curvatures of the Brønsted plots are interpreted in terms of an entropic contribution to the position of the transition state.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030206
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  • 9
    Electronic Resource
    Electronic Resource
    Gas-phase nitration of thiophene and N-methylpyrrole by protonated alkyl nitrates (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 110-118 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas-phase nitration of thiophene (1) and N-Methylpyrrole (2) was studied by radiolytic tecniques, supported by chemical ionization mass spectrometry. The substrate and positional selectvities of protonated alkyl nitrtes (CH3NO3H+, CF3CH2NO3H+) were deduced from competitive reactions with bezene performed under different conditions. The apparent kS/kB ratios, which are independent of the pressure and unaffected by the presence of a strong base (NEt3), depend on the nature of the electrophile, passing for 1 and 2 from 7·2 and 6·4, respectively, with CH3NO3H+ to 1·1 and 1·0, respectively, with the more reactive fluorinated caution. Predominant (88%) α-substitution takes place in 1, whereas no appreciable positional discrimination is displaced by 2. The results suggest that the electrophilic attack can also occur a the heteroatom, and point to the same mechanism postulated for gasphase nitration of aromatic substrates, the reactivity being essentially governed by electrostatic interactions within the ‘encounter pair’.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030207
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  • 10
    Electronic Resource
    Electronic Resource
    Role of 2-carboxyl substituent in the tautomerization between two equivalent enol forms of 3-hydroxyphenalenone (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 485-488 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The interconversion between two equivalent enol forms of 3-hydroxyphenalenone took place predominantly through a diketo form with a free energy of activation of ca 14 kcal mol-1 in DMSO solution determined by 125·8 MHz13C NMR measurement. On the other hand, the corresponding interconversion in 2-carboxy-3-hydroxyphenalenone was not frozen on the time scale of 13C NMR spectroscopy down to -60°C. This acceleration in the interconversion rate of the latter may be interpreted by a double proton switching between the hydrogen-bonded 2-carboxyl and 3-hydroxyenone moieties.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030712
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