Ligação covalente coordenada boro-nitrogênio : um estudo comparativo entre moléculas derivadas do etano, eteno e etino orgânicos e inorgânicos

Abstract

This work consists in the theoretical analysis and comparison of some organic compounds and its similar inorganics, through the change of the BN pair, and, in some cases, the BP pair, in the place of CC pair. First, ethane, ethene and ethine molecules, organic (with CC pair) and inorganic (with BN and BP pairs), were analysed; they worked as reference for the analysis of organic and inorganic (here, just BN pair) functionalized molecules (ethanol, ethenol and ethanal, ethanoic acid and ethenediol, ethylamine, ethylbenzene, propane and fluoroethane). For ethane, ethene and ethine molecules, dipole moment, population analysis, energy, bond length and molecular orbitals were analysed. In this case, the DFT method (with b3- lyp and pwlda functionals) and HF method were used. For the molecules with functional group (CC and BN), energy, bond length, bond order and a comparison between isomers were done. Here, DFT (b3-lyp) and CC2 methods were used. For all calculations we used TURBOMOLE. So, it was verified that the dipole moment of the reference molecules follows the same tendency of the Löwdin population analysis (corroborating with the idea of the donation of the electrons pair from the basis to the acid – Lewis acid/basis). This analysis presents results coherent with the chemical feeling, although it has limitations because it concentrates the charges over the atoms. For the molecules with functional groups, we verify a bigger bond length, smaller bond energy and smaller bond order (“main” bond) for the inorganic molecules (dative bond) when comparing to organic molecules (common covalent bond). Besides that, BN molecules are more stable than NB ones, although the bond energy of BN molecules is smaller than of the NB ones. And, also, the analysis of bond strength, bond energy and bond order for the B-N bond showed that the functional groups sequence is different according with each inorganic isomer (BN or NB). So, just the analysis of the electronegativity or bond strength doesn’t necessarily lead to correct values of acidity.