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  • Carbonyl derivatives  (2)
  • Analytical Chemistry and Spectroscopy  (1)
  • 2000-2004
  • 1995-1999  (3)
  • 1955-1959
Collection
Keywords
Publisher
Years
  • 2000-2004
  • 1995-1999  (3)
  • 1955-1959
Year
  • 1
    Electronic Resource
    Electronic Resource
    Ab Initio studies on the rotational equilibria of 2-substituted furan and thiophene carbonyl derivatives (1996)
    Springer
    Theoretical chemistry accounts 93 (1996), S. 199-210 
    Details
    ISSN: 1432-2234
    Keywords: Rotational isomer ; SCRF ; Furan ; Thiophine ; Carbonyl derivatives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The relative stabilities of syn- and anti-isomers of 2-substituted furan and thiophene carbonyl derivatives are investigated by theab initio MO method. The energy differences between the rotamers are 1–3 kcal mol−1 but the barriers to rotation are ca. 10 kcal mol−1 so that free rotational mode is predicted to be a rather difficult process. Application of the self-consistent reaction field (SCRF) method to account for the solvent effect indicates that the isomer with a higher dipole moment (syn) is favored in solution. An electron withdrawing 2-substituent favors syn-isomers for furan carbonyls in contrast to thiophene carbonyls for which anti-isomers are favored. These trends are ascribable to a decrease in electrostatic repulsive and attractive interactions, respectively, in the syn forms of furan and thiophene carbonyls. Contribution of non-bonded repulsive interaction in the anti-isomer is important for the relative stability of the syn-isomer of furan carbonyl derivative. Solvent effects due to higher dielectric continuum are small on the absolute values of energy differences but can reverse the order of stability of the two isomers due to a greater stability acquired by an isomer (syn) with higher dipole moment in solution. The major factor determining stability, or instability, of syn-isomer is a repulsive electrostatic interaction between the two oxygen atoms for furan carbonyls and an attractive electrostatic interaction between the sulfur and oxygen atoms for thiophene carbonyls.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113417
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  • 2
    Electronic Resource
    Electronic Resource
    Ab Initio studies on the rotational equilibria of 2-substituted furan and thiophene carbonyl derivatives (1996)
    Springer
    Theoretica chimica acta 93 (1996), S. 199-210 
    Details
    ISSN: 0040-5744
    Keywords: Key words: Rotational isomer ; SCRF ; Furan ; Thiophine ; Carbonyl derivatives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  The relative stabilities of syn- and anti-isomers of 2-substituted furan and thiophene carbonyl derivatives are investigated by the ab initio MO method. The energy differences between the rotamers are 1–3 kcal mol-1 but the barriers to rotation are ca. 10 kcal mol-1 so that free rotational mode is predicted to be a rather difficult process. Application of the self-consistent reaction field (SCRF) method to account for the solvent effect indicates that the isomer with a higher dipole moment (syn) is favored in solution. An electron withdrawing 2-substituent favors syn-isomers for furan carbonyls in contrast to thiophene carbonyls for which anti-isomers are favored. These trends are ascribable to a decrease in electrostatic repulsive and attractive interactions, respectively, in the syn forms of furan and thiophene carbonyls. Contribution of non-bonded repulsive interaction in the anti-isomer is important for the relative stability of the syn-isomer of furan carbonyl derivative. Solvent effects due to higher dielectric continuum are small on the absolute values of energy differences but can reverse the order of stability of the two isomers due to a greater stability acquired by an isomer (syn) with higher dipole moment in solution. The major factor determining stability, or instability, of syn-isomer is a repulsive electrostatic interaction between the two oxygen atoms for furan carbonyls and an attractive electrostatic interaction between the sulfur and oxygen atoms for thiophene carbonyls.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113417
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  • 3
    Electronic Resource
    Electronic Resource
    Separation of Positional Isomers on A, C- and A,D-Bridged Calix[6]arene as Stationary Phases in Capillary GC (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 679-682 
    Details
    ISSN: 0935-6304
    Keywords: A,C- and A,D-bridged calix[6]arene ; stationary phase ; capillary gas chromatography ; geometric and positional isomer separation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A,C-Bridged (ACCX) and A,D-bridged isopropyldimethylsilylcalix[6]arene (ADCX) dissolved in OV-1701 were used as stationary phases in isothermal capillary gas chromatographic separation of some positional isomers. Retention factors and separation factors for the isomers were measured. The isomers investigated are well resolved on the two phases. Retention of all the solutes investigated is longer on ACCX than on ADCX. The longer retention on A,C-bridged calix[6]arene is probably due to extra inductive interactions of the solute molecule with the carbonyl moieties in the phase. Separation factors for closely eluting isomer pairs are similar on the two phases. This seems to indicate that the carbonyl moieties do not play an appreciable role in discriminating the isomer molecules on entering the cavity of the calixarene if the solute is retained by the inclusion process.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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