Avaliação de diferentes métodos de cálculo de propriedades magnéticas na atribuição inequívoca dos sinais de RMN e da estereoquímica relativa do a-epoxipineno e da 1,6-epoxicarvona
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2009-08-27
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Queiroz Júnior, Luiz Henrique Keng
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Universidade Federal do Espírito Santo
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The work discussed here aims to use theoretical calculations of the shielding tensors (?)and spin-spin couplingconstants(J)through different theoretical methods(GIAO, CSGT, IGAIM and SGO), in order to make a comparative study of the methods in question, and use the data obtained through these as an auxiliary tool to allow an unequivocalassignment ofboth allof 1H andof 13C NMR signals andthe relative stereochemistry of epoxides.This study focusesontwo compounds, ?-epoxypinene and 1,6-epoxycarvone, characterized by having an oxirane ring, one of the most versatile functional groups within organic chemistry. Compounds of this group are often used as intermediates in the synthesis of natural products, which brings out the importance on studiesof substances belonging to this class.After being arranged in tables, a statistical work was done in order to correlate the experimental data with the theoretical. By examining the standard deviation (SD), mean deviation (MD),linear correlation coefficient (R) and subtleties, that is, some very divergent values between the cisand transisomer, it was possible to assign unequivocallythe 1H and13C NMR signals, and the transstereochemistry for the ?-epoxypinene andthe 1,6-epoxycarvone. It was found that the theoretical values of the NMR chemical shifts obtained with the DFT/B3LYP theory level and CSGT and IGAIM methods applied to calculate the 1H and13C NMRshielding tensors (chemical shifts) of these compounds allow anexcellent correlation with experimental values, and let us associate a low computational cost with ahigh accuracy of the results found.
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QUEIROZ JÚNIOR, Luiz Henrique Keng. Avaliação de diferentes métodos de cálculo de propriedades magnéticas na atribuição inequívoca dos sinais de RMN e da estereoquímica relativa do a-epoxipineno e da 1,6-epoxicarvona. 2009. Dissertação (Mestrado em Química) – Universidade Federal do Espírito Santo, Vitória, 2009.