Theoretical Study On The Aromaticity Of Planar Heterocyclic Aromatic Compounds

This paper contained three sections in all. We mainly studied the aromaticity of planar heteroring compounds from geometric, energetic, and magnetic aspects, and different criteria to evaluate aromaticity were also compared.In the first section, we used bond-length equalization, aromaticity stabilization energy (ASE) and nuclear independent chemical shift (NICS), calculated with (density functional theory) B3LYP levels at the 6-311+G** basis set, to evaluate the aromaticity of five-member C-containing rings and their Si-, N-, and P-substituted aromatic heterocyclics. The result revealed statistically significant correlations among the above three criteria. In the second section, we used two classical magnetic criteria, magnetic susceptibility (MS) and NICS, calculated with B3LYP levels at the 6-31G** basis set, to evaluate aromaticity of planar bicyclicπ-electron systems: naphthalene and its mono- and di- aza- and phospha- derivatives. The result showed significant collinearity of the above two magnetic criteria when evaluating N-containing naphthalenes, but did not speak with the same voice when evaluating P-containing naphthalenes. Thus, we could conclude that magnetic susceptibility is a reliable criterion and NICS is not in our case.In the last section, we used HOMA (Harmonic Oscillator Model of Aromaticity), NICS and AIM (Atom in Molecule), calculated with B3LYP levels at the 6-311G(d,p) basis set, to study aromaticity of the individual rings of 2,6-dithiopurine and its tautomers in gas phase and water phase. The result showed statistically significant correlation consistency among the above criteria. And more importantly, some conclusion drawn from this part would supply us a good reference for our further research.