The work described in this thesis is concerned with three areas which are the generation of stable carbocations from saturated model compounds related to poly- vinylidenefluoride, the development of synthetic routes to fluoro-organo-phosphazenes with intention of obtaining some potential additives for perfluoropolyether fluids operating at elevated temperatures, and pericyclic reactions involving fluorinated olefins.1. We reported that some remarkable conjugated cations, and di-cations (4a) are obtained by reaction of hydrofluorocarbon precursors (4) with an excess of antimony pentafluoride. Cations (4a) bear the fluorine atoms at the charged sites, which of course, leads to stabilisation of the systems We investigated the effect of both re-hybridisation and charge on (^13)C, (^19)F, (^1)H n.m.r. chemical shifts and we applied the empirical criterion of (^13)C chemical shifts additivity to these systems to confirm the structure of some carbo-mono-cations and.-di- cations.2. The mechanism of displacement reactions in halophosphazenes was rationalised by reacting the systems in study with selected nucleophiles in competition reactions. Some fluoro-organo-phosphazenes were synthesised using halophosphazenes as starting materials. Different methodologies were used and their effectiveness was limited by the reactivity of the halophosphazenes towards the fluoroalkylating agents. The methodologies used include nucleophilic displacement of the halogen with fluorinated alcohols (R(_F)CH(_2)OH), and perfluoroalkylating agents (eg.: CF(_3)SiMe(_3)); perfluoroalkylation of organo-phosphazene using hexafluoropropene under gamma ray irradiation. Potential stabilising agents for perfluoropolyether fluids were synthesised and their effectiveness was tested.3. Some pericyclic reactions of heptafluorobut-2-ene and hexafluorobut-2-ene with dienes have been studied in an attempt to synthesise a series of benzenoid and heteroaromatic compounds containing two trifluoromethyl groups in high yields.

The primary goal of the research described in this thesis concern the synthesis, characterization and study of 1,8-bis(diarylmethylium)naphthalenediyl dications. Such dications have been prepared from the corresponding diols and have been fully characterized. Single crystals X-ray diffraction studies indicate that the two cationic centers of these derivatives are separated by 3.0 - 3.1 ??. The enforced proximity of the cationic centers intensifies the electron deficiency of these derivatives which behave as strong organic oxidants. As indicated by cyclic voltammetry, these dications undergo a two-electron reduction to afford the corresponding acenaphthenes. The newly formed C-C bond which links the former methylium are remarkably long (1.628-1.706 ??.) and can, in some instances, be oxidatively cleaved in the presence of acids. These dications can also be reduced chemically by reducing reagent, such as hydride, chloride, bromide and iodide. Remarkably, the reaction of 1,8-bis(diphenylmethylium)naphthalenediyl dication with fluoride anion results in the formation of a mono fluorinated cation which features an unsymmetrical C-F?C bridge between the former methylium centers. As indicated by 1H NMR spectroscopy, the structure of this cation is fluxional with the fluorine atom oscillating between the former methylium centers. Finally, this thesis also deals with the synthesis and study of 4,6-bis(dimesitylboryl)dibenzofuran and isoelectronic dications.

Thesis (M. Sc.)--York University, 2001. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references (leaves 85-90). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ71609.

Thesis (Ph.D.) -- McMaster University, 1999. / Includes bibliographical references (leaves 260-271). Also available via World Wide Web.

Thesis (Ph.D.) -- McMaster University, 1999. / Includes bibliographical references (leaves 149-161). Also available via World Wide Web.

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Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2013-04-23T12:16:29Z No. of bitstreams: 1 Jose Silva.pdf: 734957 bytes, checksum: 1ef37b8965ca5ceae7b3d5d5cf6b915c (MD5) / Made available in DSpace on 2013-04-23T12:16:29Z (GMT). No. of bitstreams: 1 Jose Silva.pdf: 734957 bytes, checksum: 1ef37b8965ca5ceae7b3d5d5cf6b915c (MD5) Previous issue date: 2004 / O propósito deste trabalho é mostrar que a ressonância não-sincronizada pode representar a deslocalização das ligações sigma em carbocátions, possibilitando uma descrição dos carbocátions com ponte mais articulada com outros conceitos da química. A tese é composta de duas partes, em dois níveis conceituais: a transposição do conceito de híbrido de ressonância não-sincronizada, da química de estado sólido para a química orgânica, e a avaliação da qualidade da transposição realizada, através de seu emprego na explicação do cátion C4H7+. A partir da constatação de que as regras de ressonância não-sincronizada podem ser aplicadas aos carbocátions, é formulada uma inter-relação destes conceitos. Os íons não-clássicos tornam-se, então, um caso particular de ressonância não-sincronizada de ligações. Estabelecida a relação conceitual entre íons não-clássicos e ressonância não-sincronizada, passa-se ao exame da estrutura interna desta relação, através de um estudo de caso. A crítica dos trabalhos que buscaram identificar a estrutura do cátion C4H7 + ? através de reações solvolíticas, de cálculos de geometria e energia e, de espectroscopia de RMN em soluções superácidas e sobre matriz superácida sólida ? revela a incerteza dos resultados teóricos e experimentais, que são reinterpretados como um complexo equilíbrio químico entre isômeros híbridos de ressonância não-sincronizada. O estudo do caso do cátion C4H7+ demonstra a potencialidade da ressonância não-sincronizada para explicar a deslocalização de ligações sigma nos carbocátions em geral. Desse modo, é sugerido que os problemas da descrição e da representação dos carbocátions com ponte encontram uma solução na ressonância não-sincronizada. Como conseqüência, os íons não-clássicos não podem ser mais considerados como anomalias, revelando-se tão clássicos quanto quaisquer outros carbocátions. / Salvador