Gas-phase SiCl 3 + ions undergo sequential solvolysis type reactions with water, methanol, ammonia, methylamine and propylene. Studies carried out in a Fourier Transform mass spectrometer reveal that these reactions are facile at 10 -8 Torr and give rise to substituted chlorosilyl cations. Ab initio and DFT calculations reveal that these reactions proceed by addition of the silyl cation to the oxygen or nitrogen lone pair followed by a 1,3-H migration in the transition state. These transition states are calculated to lie below the energy of the reactants. By comparison, hydrolysis of gaseous CCl 3 + is calculated to involve a substantial positive energy barrier.
2010Ficha Catalográfica Elaborada pela Divisão de Biblioteca e Documentação do Conjunto das Químicas da USP. AGRADECIMENTOSAo prof. Dr. José Manuel Riveros pela cuidadosa, atenciosa e precisa orientação, tornando a execução desse trabalho muito prazerosa ao longo desses dois anos.Ao Jair João Menegon pelo suporte técnico concedido nos momentos cruciais aos equipamentos do laboratório e pelas conversas agradáveis tanto científicas como não científicas durante os cafés da tarde.Ao Thiago Carita Correra pelas importantes e calorosas discussões científicas e pela ajuda em diversas situações. In this dissertation, we present some new results on the gas-phase reactivity of the + SiCl 3 ion with a number of simple n electron donor bases such as water, alcohols, ammonia, amines and some electron donor bases.Ion-molecule reactions were characterized experimentally by Fourier transform ion cyclotron resonance mass spectrometry (FTICR) at pressures in the 10 -8 Torr range. Reactions were followed as a function of trapping time of the ions in the cell of the spectrometer and this allowed for the identification of subsequent reactions of the primary product ions. The energy diagram and structure of the different silicenium ions were also characterized by computational chemistry using both ab initio and density functional theory methods in order to understand the mechanism of these reactions. +SiCl 3 reacts rapidly in gas phase with various neutral substrates through processes similar to solvolysis in which the neutral substrate adds onto the silicenium ion followed by elimination of HCl. In some cases, complete solvolysis is observed with substitution of all three chlorine atoms.The calculations show that reactions proceed by initial addition of the electrophile onto the electron center of the neutral substrates giving rise to stable adducts. The transition state for these reactions involve a 1,3hydrogen migration and the calculated energy for these transition states is less than the energy of the isolated reactants, a fact that is common to fast A extrapolação do comportamento em fase gasosa para o comportamento macroscópico em fases condensadas, embora desejável, não é uma tarefa trivial na maioria dos casos. As mudanças das propriedades termoquímicas, das cinéticas de reação e dos mecanismos em função de efeitos progressivos de solvatação, assim como efeitos devido aos contra-íons, continuam sendo um desafio tanto do ponto de vista experimental como teórico.Além dos aspectos relacionados com a compreensão das propriedades e reatividade intrínseca de íons e neutros, há outros motivos de interesse mais específicos para compreender a reatividade bimolecular e propriedades de espécies iônicas em fase gasosa. Assim, podemos citar exemplos como: 1) o uso crescente de misturas gasosas ionizadas pela indústria de semicondutores em "corrosão por plasma" (plasma etching) e deposição química a vapor por plasma (PECVD) e por plasma remoto (PECVD); 2) o papel de processos iônicos em ambientes interestelares envolvendo moléculas e ío...
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