A Theoretical and Experimental Scale of Aromaticity. The First Nucleus-Independent Chemical Shifts (NICS) Study of the Dimethyldihydropyrene Nucleus^⊥

Nucleus-independent chemical shift (NICS) values were calculated at several locations for a series of dimethyldihydropyrenes (DDPs). These NICS values were used to assess the relative aromaticities of the dimethyldihydropyrene nucleus (DDPN) of these DDPs and to construct a NICS scale of aromaticity. The NICS and experimentally determined relative aromaticities of these DDPNs are in complete agreement, verifying that NICS can be used not only to classify a compound as aromatic but also to determine the degrees of aromaticity of structurally related systems.