The induced magnetic field in cyclic molecules

The response of a molecule to an applied external magnetic field can be evaluated by a graphical representation of the induced magnetic field. We have applied this technique to four representative, cyclic organic molecules, that is, to aromatic (C₆H₆, D_6h), anti-aromatic (C₄H₄, D_2h) and non-aromatic (C ₄H₈, D_4h, and C₆H₁₂, D_3d) molecules. The results show that molecules that contain a π system possess a long-range magnetic response, while the induced magnetic field is short-range for molecules without π systems. The induced magnetic field of aromatic molecules shields the external field. In contrast, the anti-aromatic molecules increase the applied field inside the ring. Aromatic, anti-aromatic, and non-aromatic molecules can be characterized by the appearance of the magnetic response. We also show that the magnetic response is directly connected to nucleus-independent chemical shifts (NICS).