A hexagon with an inscribed circle, representing delocalised aromatic bonding.
Also known as: Aromatic ring, Hexagon with a circle, Kekulé structure
A hexagon with a circle inside means benzene's six electrons are shared around the whole ring rather than fixed in alternating bonds. The circle was introduced precisely because the alternating-bond drawing says something untrue.
Represents benzene, in which six electrons are delocalised around the ring rather than held in three fixed double bonds.
Contexts: Laboratory
Uses an inscribed circle rather than alternating double bonds because the alternating drawing implies that the bonds differ, which measurement shows they do not.
Contexts: Laboratory
Replaced the Kekulé structure of alternating single and double bonds, which is still drawn where individual electrons need to be tracked through a mechanism.
Contexts: History, Laboratory
A regular hexagon drawn in outline with a plain circle inscribed inside it, the circle not touching the sides.
Both belong to the shorthand of structural drawing.
The circle notation exists to avoid needing resonance arrows between Kekulé forms.