Aromaticity of C20H10-xFx Corannulene: A Comparative Study by NICS and EFG Methods

Abstract

Corannulene (C20H10) and its fluorinated derivatives, C20H10-xFx (x=1-10), are investigated at the B3LYP/6-31G level of density functional theory. The degree of electron delocalization is evaluated using Nucleus Independent Chemical Shift (NICS) method, Electric Field Gradient (EFG) method and factor of Ellipticity (ε). In this study, the benzene is the scale of comparison as a more aromatic structure. The aromaticity has been evaluated at three points of structures; center of five-member ring (5-MR), center of fluorine-substituted ring (6-MR), and center of other six-member rings. This comparison shows that substitution of fluorine for four and five hydrogen atoms in the Corannulene structure, C20H10-xFx (x=4, 5), results in more aromaticity compared to the other substitutions, and C20H10 and C20H10-xFx (x=1, 3) are more antiaromatic. It seems that the EFG method is more reliable for forecasting the aromaticity of structures, than NICS method. The factor of Ellipticity and bond lengths resulted from Atom in Molecule (AIM) analysis support the EFG method.