Comparing Methods for Calculating Aromaticity of Oxocarbons with Different Ring Sizes and Charges

Event Center A & B

There are many computational methods used to determining aromaticity. This project compares four methods used in calculating aromaticity for oxocarbons and their anions: HOMO-LUMO gap, isodesmic reactions, NICS (nucleus independent chemical shift) differences and the HOMA (harmonic oscillator model of aromaticity) method. The calculated predictors were compared to each other to see if they showed consistent trends for oxocarbons differing in ring size and charge. The four cyclic oxocarbons examined were deltic acid, squaric acid, croconic acid and rhodizonic acid, as well as their mono and di-anions. Each molecule was optimized at DFT/RB3LYP 6-311++G** in a vacuum using Spartan 10 because it was the highest bases set for all of the data collected. The results showed that isodesmic reactions and HOMO-LUMO gap didn’t work with this range of structures. Two methods, NICS-difference and HOMA, were the methods that showed consistent trends across these varied systems.