Aromaticity of ionic structures: Investigation and application of NICS value and 4n + 2 rule

Abstract

At DFT/B3LYP/6-31G** theoretical level, C6H and C (n = 0, −2, and +2), C6H and C (n = 0, ±2, ±4, and ±6), C6H (n = 0–6), as well as C6H6-A and C6-A (A = Be, B, N, O, Mg, Al, Si, S, and Fe) structures were investigated. Comparing NICS values of C6H and C (n = 0, −2, and +2), we discovered that C6H, C6H were antiaromatic, and C6H6, C6, C, C had aromaticity with negative NICS values. According to research of C6H and C (n = 0, ±2, ±4, ±6), C6H (n = 0–6), we sustained that their σ and π orbit were different and the locations of electrons were difficult to confirm in ionic structures. Thus, neither 4n + 2 rule nor NICS values can precisely estimate the aromaticity of ionic structures. Besides, through WBI (NBO) research of C6H6-A and C6-A (A = Be, B, N, O, Mg, Al, Si, S, and Fe) structures, we found that C6H6 was easy to accept electrons, contrarily, C6 was prone to bestowing electrons. Moreover, C6H6 took the symmetrical carbon atoms form feeble interaction or bond, and C6 used all carbon atoms to impact with other atom. C6H6 generated two contrapuntal single bonds with oxygen, sulfur, and nitrogen atoms, whereas C6 molecule formed double bond with oxygen and nitrogen atoms, two conjoint single bonds with sulfur atom. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010