Análisis de la aromaticidad con la teoría de Orbitales Moleculares de Hückel

Abstract

In this work, we review H¨uckel’s Molecular Orbital theory (HMO) in order to study the behaviour of some aromaticity indices (FLU, Iring, MCI and PDI) in annulenes and polyacenes in their ground state and their excited state. The simplicity of HMO enables us to understand the behaviour of these indices and to explain the aromaticity values obtained within this theory. To perform the calculations, we have created a program using Fortran language, which also has been useful to learn about the aromaticity indices and how programming works. The results obtained from this program have been analysed by representing the indices values against the molecule size, with the aim to test how aromaticity and antiaromaticity increase or decrease with the number of atoms in the molecule. In the case of annulenes, we have compared those results with H¨uckel’s and Baird’s rules predictions to see if they fit with our data. We have seen that Baird’s rule seems not to be fulfilled in some cases. However, we have been able to see that H¨uckel’s and Baird’s rules fade away in a very similar way as we increase the ring size. Finally, because of the limitations of the HMO theory, we will show that the results have to be contrasted with more advanced calculations.