No / The reactions of ionised pyridazine, aminopyrazine and aminopyridine and the corresponding ¿-distonic ions are examined by a combination of tandem mass spectrometric techniques, including analysis of metastable ion (MI), collision induced dissociation and neutralisation¿reionisation mass spectra (NRMS). Further insight into the relative stability and energy barriers towards tautomerism of each ionised heterocycle with its ¿-distonic isomer is obtained by computational methods. In all these systems, both the conventional radical-cation and the ¿-distonic tautomer are stable species which exist in discrete energy wells, with a significant barrier towards their interconversion. Although each ¿-distonic ion is sufficiently stable to survive neutralisation¿reionisation, the conventional ionised heterocycle is more stable in each case. The possibility of investigating proton-transport catalysis in the tautomerism of these ionic systems is discussed.

Orientador: Nelson Henrique Morgon / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-12T17:33:08Z (GMT). No. of bitstreams: 1 Lima_JoseCarlosBarretode_M.pdf: 1046152 bytes, checksum: 5cac61f65804d91e30491970eb62e5a9 (MD5) Previous issue date: 2008 / Resumo: O principal objetivo deste trabalho foi analisar quatro mecanismos teóricos para a redução (em fase gasosa) do ácido acético a etanol. Foi empregado NaBH4 na presença de um eletrófilo (H2SO4). Todos os cálculos foram realizados com a teoria CBS-QB3 usando o programa Gaussian 98. Foi observado que esta metodologia teve sucesso em predizer afinidades por próton e por elétron em um custo computacional mais baixo. A comparação entre seis teorias (CBS-4M, CBS-QB3, G2(MP2), G3(MP2), G2 e G3) usando uma análise estatística através do valor médio, do desvio padrão e da raíz média quadrática, mostrou um desempenho melhor da teoria CBS-QB3 para obter as propriedades. Uma metodologia geral foi proposta baseada nos resultados teóricos para as propriedades estruturais (comprimento do ângulo e da ligação) e termodinâmicas (variação da energia livre e da entalpia). As estruturas obtidas para mínimo local e para estados de transição na superfície da energia livre foram analisadas, bem como a consideração de efeitos solventes com um modelo contínuo (PCM) / Abstract: The main objective of this work was to analyze four theoretical mechanisms to the reduction (in gas-phase) of acetic acid to ethanol. It was employed NaBH4 in presence of an electrophile (H2SO4). All the calculations were carried out at CBSQB3 method using the Gaussian 98 program. It was found that this methodology suceeds in predicting proton and electron anities at a lower computational cost. The comparison among six theories (CBS-4M, CBS-QB3, G2(MP2), G3(MP2), G2 and G3) using statistical analysis, evaluating average value, standard deviation and root-mean-square, showed a better performance of CBS-QB3 to obtain the properties. A general methodology was proposed based on the theoretical results of structural (angle and bond length) and thermodynamics (enthalpy and free energy variation) properties. Structures of minimum and transistion states on the free energy surface were analyzed, and the inclusion of solvent effects with a continuum model (PCM) / Mestrado / Físico-Química / Mestre em Química