Nucleus independent chemical shifts (NICS) scan method analysis for cyclic oxocarbons
Mentor:Kimberley Cousins, Professor of Chemistry, California State University San Bernardino
Research on croconic acid has shown that the single crystal form has ferroelectric properties. The aromatic character of the molecule was being analyzed to determine whether aromaticity was a contributing factor to the ferroelectric behavior. Three other oxocarbon analogs, as well as their mono- and dianions, were also studied to determine if they had aromatic properties as well. This project used the nucleus independent chemical shifts (NICS) scan method to evaluate the aromaticity of the four cyclic oxocarbon compounds: deltic, squaric, croconic, and rhodizonic acid. The aim was to provide a more accurate analysis by placing ghost atoms 0.1 Å apart to a height of 3.0 Å. Non-conjugated analogues of each of the conjugated molecules were also analyzed for comparison. The molecules had their geometries optimized using Spartan 10 using the density functional method B3LYP/6-311+G**. The NICS scan calculations were performed using GAMESS. Graphs of the results showed that minima did not all occur at the height of 1 Å, the height at which the previous values were reported; for example, the neutral deltic molecule had a minimum of -27.8567 at a height of 0.2 Å. The differences between the minima for the conjugated and non-conjugated molecules were then graphed to remove ring size effects from the observed shielding. There were new minima determined for the smaller, three-membered rings, with a difference of 15.1836 between the NICS scan determined minimum value and the difference value. This indicates that previous conclusions overestimated the aromaticity of the deltic systems.