A complete theoretical study for the novel selenocarboxylic acids, RC(O)SeH (R = CH3, CHF2, CClF2 y CF3): Energetic, conformational and vibrational properties, gas phase acidity and dimerization

JOVANNY A. GÓMEZ CASTAÑO; ROSANA M. ROMANO; CARLOS O. DELLA VÉDOVA

Isla San Andrés, Colombia

Congreso; XXXV Congreso de Químicos Teóricos de Expresión Latina QUITEL; 2009

Recently we have attained the synthesis of the novel selenocarboxylic acids RC(O)SeH (R= CH3, CHF2, CClF2 y CF3) by the Se/O exchange reaction in sealed conditions betweenthe corresponding carboxylic acid, RC(O)OH, and the Woollins reactant.[1] Besides anextensive physicochemical and spectroscopic characterization, these new compounds were also theoretically studied using ab initio and DFT methods. In this work we present a compendium of the results obtained from different theoretical methods.3, CHF2, CClF2 y CF3) by the Se/O exchange reaction in sealed conditions betweenthe corresponding carboxylic acid, RC(O)OH, and the Woollins reactant.[1] Besides anextensive physicochemical and spectroscopic characterization, these new compounds were also theoretically studied using ab initio and DFT methods. In this work we present a compendium of the results obtained from different theoretical methods. For all the selenocarboxylic acids studied in this work the energetically most stable form corresponds to a conformation in where the dihedral angle H-Se-C=O is oriented in syn position (0,0 °), while an anti orientation (180,0 °) corresponds to a less stable form. For acids with different atoms in the methyl group, R = CHF2 and CClF2 a gauche orientation is the most stable spatial arrangement for the chain O=C-C-X (X = H or Cl). The IR spectra and thermochemical properties for all the theoretical stable forms were also calculated and the results compared with the FTIR matrix isolation spectra measured at different temperatures. With the assistance of the theoretical results two rotamers for the compound CH3C(O)SeH, CF3C(O)SeH and CHF2C(O)SeH and three rotamers for the compound CClF2C(O)SeH were detected in the FTIR spectra. The relative distribution of the concentration in gas phase, at room and higher temperatures, were also estimated in each case. Because the chemical nature and instability against moisture of these new selenocarboxylic acids, we calculated its gas phase acidity theoretically. The results were compared with those obtained, using the same theoretical approximations, for its corresponding less heavy congeners RC(O)OH and RC(O)SH we found a more acid strength for the acids RC(O)SeH. Regarding the dimerization of the acids RC(O)SeH, a cyclic symmetric structure correspond in all cases to the most stable dimer form. Other less stable dimmers with asymmetric structure, were also predicted theoretically. The stabilization interactions between the subunits RC(O)SeH in each dimer (RC(O)SeH)2 were studied by a “donoracceptor” model using NBO analysis. Because the chemical nature and instability against moisture of these new selenocarboxylic acids, we calculated its gas phase acidity theoretically. The results were compared with those obtained, using the same theoretical approximations, for its corresponding less heavy congeners RC(O)OH and RC(O)SH we found a more acid strength for the acids RC(O)SeH. Regarding the dimerization of the acids RC(O)SeH, a cyclic symmetric structure correspond in all cases to the most stable dimer form. Other less stable dimmers with asymmetric structure, were also predicted theoretically. The stabilization interactions between the subunits RC(O)SeH in each dimer (RC(O)SeH)2 were studied by a “donoracceptor” model using NBO analysis. Because the chemical nature and instability against moisture of these new selenocarboxylic acids, we calculated its gas phase acidity theoretically. The results were compared with those obtained, using the same theoretical approximations, for its corresponding less heavy congeners RC(O)OH and RC(O)SH we found a more acid strength for the acids RC(O)SeH. Regarding the dimerization of the acids RC(O)SeH, a cyclic symmetric structure correspond in all cases to the most stable dimer form. Other less stable dimmers with asymmetric structure, were also predicted theoretically. The stabilization interactions between the subunits RC(O)SeH in each dimer (RC(O)SeH)2 were studied by a “donoracceptor” model using NBO analysis. Because the chemical nature and instability against moisture of these new selenocarboxylic acids, we calculated its gas phase acidity theoretically. The results were compared with those obtained, using the same theoretical approximations, for its corresponding less heavy congeners RC(O)OH and RC(O)SH we found a more acid strength for the acids RC(O)SeH. Regarding the dimerization of the acids RC(O)SeH, a cyclic symmetric structure correspond in all cases to the most stable dimer form. Other less stable dimmers with asymmetric structure, were also predicted theoretically. The stabilization interactions between the subunits RC(O)SeH in each dimer (RC(O)SeH)2 were studied by a “donoracceptor” model using NBO analysis.