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ThesisUniversity of Iceland>Verkfræði- og náttúruvísindasvið>Meistaraprófsritgerðir>

Please use this identifier to cite or link to this item: http://hdl.handle.net/1946/3434


Conformational behaviour of substituted silacyclohexanes


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.


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