NICS Difference Determination of Relative Aromaticity

commonly occur in pharmaceuticals, fuel additives, and polymers. Key characteristics that make up an aromatic structure are the delocalization of pi electrons, particular stability of the structure, and the distinct electronic field generated, which can be detected by running an NMR analysis. NICS (Nucleus Independent Chemical Shifts) is the computational method for predicting the NMR signals at certain points in space. In this Project, NICS differences between a given structure and a reference structure are investigated. NICS values are obtained using four programs: (1) Spartan to build the molecules and optimize structures; (2) Avogadro 1.2.0 to insert probe/ghost atoms(points in space that experience shielding calculations) for NICS, and to generate a GAMESS (General Atomic and Molecular Electronic Structure System) file; (3) a text editor to properly set up GAMESS input file; and (4) Submission to GAMESS via the GAMESSQ interface, to calculate shielding values for NICS. NICS scans method has taken criticism for not being able to predict the relative aromaticity of rings of different sizes and charges. By taking the difference between NICS scan values at every 0.1 angstrom intervals from the origin 0.0 angstroms (center of the ring) up to 3 angstroms, for the structure in question and its corresponding reference structure, the NICS scan method is improved. Results for benzene, benzene distortions, and multi-ring systems (including naphthalene, and phenanthrene) demonstrate the improved ability of NICS in predicting relative aromaticity. This further increasing our ability to predict aromaticity in new structures. (NSF-HRD-1345163