Simple and Effective Identification of Local 6π- and Global [4n+2] Aromaticity of Macrocyclic Conjugated Hydrocarbons by 1H/13C Chemical Shifts and the Corresponding Ring Current Effect

Structures, H-1/C-13 chemical shifts, and the ring current effects (spatial magnetic properties: through-space NMR shieldings [TSNMRSs]) of various pi-conjugated macrocyclic hydrocarbons and the corresponding charged analogues have been calculated at the B3LYP/6-311G(d,p) theory level using the GIAO perturbation method and employing the nucleus-independent chemical shift (NICS) characterization. The spatial magnetic properties (TSNMRS) are visualized as iso-chemical shielding surfaces (ICSSs) of various size and direction and together with especially the delta(H-1)/ppm chemical shifts employed to unequivocally qualify and quantify local 6 pi-aromaticity of individual benzenoid building blocks and the global ([4n + 2], n > 1) aromaticity of the macrocyclic ring.