Evaluation of the aromatic character of some bowl shape polycyclic carbon nanostructures

In two recent decades, nucleus independent chemical shift (NICS) criterion was used to gauge the amount of aromaticity of organic and inorganic compounds in a lot of publications. In this study, aromatic, nonaromatic and antiaromatic character in different rings of coronene (C24H12) ,corannulene (C20H10), sumanene (C21H12) and circumtrindene (C36H12) bowl-shaped nanostructures, which are fullerene (C60) substructures was evaluated by this criterion. In the first, structures were optimized at B3LYP/6-311(d,p) level of theory and then analytical frequency calculations were done at the same level to ensure achieving the correct structures. NMR calculations were also done at the same level of theory to determine the magnetic shielding tensors in order to calculating NICS and NICSzz at the polygon surface and 1 Å above and below it for different rings of each molecule. These parameters were used to discuss local aromaticity, nonaromaticity and antiaromaticity character and were also used to determining overall aromaticity character of aforesaid four molecules. Results showed that NICS or NICSzz values are more negative for concave face than convex face for each molecule. Average of the NICSzz for coronene, corannulene, sumanene and circumtrindene molecules are equal to -21.57, -7.46, -16.13 and -0.52, respectively, therefore coronene and sumanene are very aromatic, corannulene is slightly aromatic and circumtrindene is nonaromatic.