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  • Conformational behaviour of substituted silacyclohexanes
  • Rannsóknir á stellingajafnvægi setinna silacyclohexan afleiða
  • Meistara
  • The monosubstituted silacyclohexanes; C5H10SiHX with X = F, Cl, Br, I, SiH3, OMe,
    N(Me)2, tBu, CN and N3 (3-12) were synthesized with the main aim of investigating
    the molecular structure of their axial and equatorial chair conformers as well as the
    thermodynamic equilibrium between these species. These derivatives were intended
    for investigations by means of gas electron diffraction (GED), dynamic nuclear
    magnetic resonance (DNMR) and temperature dependent Raman spectroscopy. This
    work is an ongoing project and has as of yet not been completed for all the
    derivatives. When possible these experimental results in the gas and liquid phase
    were compared to the quantum chemical calculations available (MP2, DFT and
    composite methods) and to results for analogous cyclohexane derivatives. The A
    values for the monosubstituted silacyclohexanes were found to be substantially lower
    than for the corresponding cyclohexane analogues and in all cases except for one,
    they show a preference of the axial conformation.
    The following 1,1-disubstituted silacyclohexane rings, C5H10SiXY with X = Me and
    Y = F, X = Me and Y = CF3 as well as X = SiF3 and Y = F (13, 14 and 16) were
    also synthesized, so as to be investigated with respect to their conformational
    properties, using the same methods as described above. C5H10SiXY with X = Me and
    Y = D (15) was synthesized in order to be investigated by Raman spectroscopy to
    complete the investigation of C5H10SiHMe (1). The available results indicate that a
    simple additive model, which assumes that the conformational properties derived
    from the relevant monosubstituted rings are either complementary or competitive,
    cannot be applied and more sophisticated model is required.
    CF3Me2SiSiMe2CF3 (17) was synthesized and its seemingly unusual conformational
    properties were investigated by gas electron diffraction (GED), temperature
    dependent Raman spectroscopy and quantum chemical calculations (QC). The results
    indicate that there is only one conformer in the gaseous phase, while three rotamers
    were observed in the liquid phase. The novel compounds (C5H10SiH)2NMe (19) and
    (C5H10SiH)2NH (24) were also synthesized and the process of conformational
    analysis was initiated by performing preliminary QC calculations.

  • 12.9.2008

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