Aromatic ring current

This article is about chemistry and physics of aromatic compounds. For the meteorological effect, see Ring current.
A diagram of an aromatic ring current. B0 is the applied magnetic field, the red arrow indicating its direction. The orange ring shows the direction of the ring current, and the purple rings show the direction of the induced magnetic field.

An aromatic ring current is an effect observed in aromatic molecules such as benzene and naphthalene. If a magnetic field is directed perpendicular to the plane of the aromatic system, a ring current is induced in the delocalized π electrons of the aromatic ring.[1] This is a direct consequence of Ampère's law; since the electrons involved are free to circulate, rather than being localized in bonds as they would be in most non-aromatic molecules, they respond much more strongly to the magnetic field.

The ring current creates its own magnetic field. Outside the ring, this field is in the same direction as the externally applied magnetic field; inside the ring, the field counteracts the externally applied field. As a result, the net magnetic field outside the ring is greater than the externally applied field alone, and is less inside the ring.

  1. ^ The induced magnetic field in cyclic molecules. Merino, G.; Heine, T.; Seifert, G. Chem. Eur. J.; 2004; 10; 4367-4371. doi:10.1002/chem.200400457