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Title: Steric and electronic effects on the structures of substituted silicon compounds
Author: McLachlan, Lorna J.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2004
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This thesis is concerned with the application of the SARACEN method to a range of molecules with interesting structural properties and applications in industry. The gas-phase structures of a series of compounds have been obtained, combining gas-phase electron diffraction and ab initio molecular orbital theory. For each compound a series of the potential energy surface was carried out to investigate the number of conformational minima and to locate the global energy minimum. The gas-phase structures of trans-1,2-dichloro-1,2-disilylethene (1), 1,1-bromosilylethene (2) and 1,1,1,4,4,4-hexachloro-1,4-disilabutane (3) were studied and ab initio calculations on analogous compounds were carried out. This study revealed extreme asymmetry in coordination at carbon, and trends in bond lengths and angles were interpreted in terms of cumulative electronic and steric contributions. The structure of bistrichlorosilyldimethylgermane [(Me2Ge(SiCl3)2] (4) was determined ab initio and by gas-phase electron diffraction and compared to that of a previously determined trimethyl analogue. An important difference between experimental and theoretical results was revealed. Three silylhydrazines, F3SiN(Me)NMe2 (5) and F3SiN(SiMe3)NMe2 (6) ClH2SiN(Me)NMe2 (7), have been studied ab initio and by gas-phase electron diffraction. Previous solid- and gas-phase investigations of other substituted silylhydrazines revealed unusually narrow Si-N-N bond angles. Structural investigations were initiated for the halogen and bulky alkyl-substituted compounds to gauge the effects of these different substitutions on the Si-N-N bonds angles. Further calculations were carried out on similar compounds upon removing the “donor” and “acceptor” atoms, to verify the presence of suspected Si β-N interactions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available