Electronic delocalization and aromaticity: computational study of hidrocarbons and POMs

Identifier:  TFG:116

Handle: https://hdl.handle.net/20.500.11797/TFG116

Authors:  De Aguirre Fondevila, Adiran Josu

Abstract:
ABSTRACT This work is devoted to the differences between delocalized and localized electrons in hydrocarbons and polyoxometalates (POMs). In the first part, we reproduce and interpret the density functional calculations in the paper[1] Chem. Eur. J. 2007, 13, 6321-6328 on benzene and ciclobutadiene. It is done using molecular fragments and carrying out different mutual rotations from the starting regular geometry. In addition, we have made a study of the nucleus-independent chemical shift (NICS) on these hydrocarbons to understand which is the role of each occupied molecular orbital on the total NICS value. The second part is focused on the POM Lindqvist anion, Mo6O192-, in different situations (different oxidation states and replacing some metal positions) to see the change in the NICS value. We are aimed at verifying, as the related bibliography states, that the NICS is a good criterion of diatropicity and diamagnetism, two measurable magnitudes that are often related to the ill-defined aromaticity. It has been proved that successive (hypothetical) reductions by 2 and 4 electrons would increase the diatropicity of the system (more negative NICS). This is a general feature of reduced POMs. We also evaluate the contribution from different orbitals to the NICS (π-orbital system in the case of benzene and HOMO and HOMO-1 orbitals in the case of POMs) to see how the change of the systems modifies the contributions from the orbitals to the total NICS. Finally, we made a more careful study splitting the contributions of each occupied orbital to see why, as seen in the literature, NICS(1) has imposed to NICS(0) as a criterion of aromaticity.