Identification of local benzenoid aromaticity and global aromaticity of polycyclic aromatic hydrocarbons (PAHs) via the corresponding ring current effects in 1H NMR spectroscopy

The spatial magnetic properties of aromatic compounds, through-space NMR shieldings (TSNMRSs, actually the ring current effect in 1 H NMR spectroscopy), of a selection of polycyclic aromatic hydrocarbons (PAHs) have been calculated using the GIAO perturbation method employing the Nucleus Independent Chemical Shift (NICS) index and visualized as Iso-Chemical-Shielding Surfaces (ICSS) of various size and direction. The deshielding belt in-plane of the aromatic moieties and around the periphery of PAHs unequivocally verifies the aromaticity of PAHs at first glance. The shielding areas above/below the plane of mono- and polycyclic aromatic moieties and/or the whole PAH characterize the extent of detectable aromaticity. Deshielding areas found at the center of the non-aromatic moieties are the internal contributions of the deshielding belt. This creates a holistic representation of the aromaticity of PAHs.