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Háskóli Íslands > Verkfræði- og náttúruvísindasvið > Meistaraprófsritgerðir - Verkfræði- og náttúruvísindasvið >

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  • Titill er á ensku Conformational behaviour of selected silicon- and germanium-containing ring systems
  • Meistara
  • Útdráttur er á ensku

    The methyl substituted germacyclohexane was synthesized and the conformational behaviour of the compound, in terms of axial and equatorial chair conformers, was investigated by means of dynamic nuclear magnetic resonance (DNMR) measurements. The result from the NMR experiment showed the axial/equatorial ratio to be 44/56 mol % at 114 K corresponding to an A value (A = Gax-Geq) of 0.06 kcal mol-1. The average free energy of activation (ΔG‡) for the temperature range 106-134 K was found to be 5.0 ± 0.1 kcal mol-1. These results are in good agreement with the quantum chemical calculated values, A value of 0.02 kcal mol-1 and ΔE of 0.01 kcal mol-1 at 0 K.
    Several compounds of monosubstituted 1,3,5-trisilacyclohexane were synthesized in order to investigate the conformational behaviour by utilizing DNMR, temperature-dependent Raman spectroscopy and gas electron diffraction (GED). Attempts to observe directly the axial and equatorial conformers by freezing the inversion on the NMR time scale failed because of the low barrier for inversion and the flexibility of the compounds. The temperature-dependent Raman measurement for methyl substituted 1,3,5-trisilacyclohexane indicated a more preference to the equatorial conformer. Results from Raman measurements for the other derivatives did not produce useful data for conformational analysis. The investigations by means of GED are still ongoing and result from these measurements are expected in the near future.
    Two monosubstituted 1-silacyclohexanes (CN and t-Bu) were also investigated with respect to their conformational properties using the same methods as described above. DNMR measurements for 1-cyano-1-silacyclohaxane showed the axial/equatorial ratio to be 35/65 mol % at 120 K corresponding to an A value of 0.14 kcal mol¬-1. The average free energy of activation (ΔG‡) for the temperature range 110-145 K was found to be 5.6 ± 0.1 kcal mol-1. The enthalpy difference from the Raman spectra for 1-tertbutyl-1-silacyclohexane indicated equatorial preference.
    During this project three 1-silacyclohexanes derivation were synthesized with the purpose to be investigated by means of dissociative electron attachment measurements. These measurements were performed by prof. O. Ingólfson's research group at the University of Iceland.

  • Rannsóknarmiðstöð Íslands, Rannís
  • 5.2.2013

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