Theoretical Predictions to pi Electron Stabilization Energy in Aromatic Compounds

Description

The aromatic stabilization energy (ASE) due to the delocalization of pi electrons in aromatic compounds has been of great interest to theoretical and organic chemists for a long time. However, even for the simplest benzene, the previously predicted ASEs are found to have great discrepancy and are dispersed in a huge energy range from ~20 to ~63 kcal/mol. The underlying reason for such discrepancy is that there is no established way to define the hypothetical localized reference structures for the ASE predictions. In this project, we propose an innovative method to build up chemically sensible localized reference structures for aromatic compounds. The localized reference structure is obtained by fully relaxed geometrical optimizations with the deletions of the overlap matrix elements for the pi and pi* orbital interactions throughout. Based on the localized reference structures, we proceed to carry out ASE predictions at the coupled cluster level and the extrapolated complete basis set limit for a series of polyaromatic hydrocarbons and heterocyclic analogs compounds of benzene. We intend to study how the electronic and geometrical effect can affect the aromatic stabilization and also correlate the ASEs with the numbers of delocalized pi electrons in the molecules. We plan to perform nucleus-independent chemical shift analysis for the localized reference structures and make critical comparisons with the fully delocalized aromatic structures.