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A double-headed straight arrow between two drawn structures.
Also known as: Double-headed arrow, Resonance
A double-headed arrow between structures means neither drawing is real: the molecule is a single thing that no one structure can depict. It is routinely confused with the equilibrium arrow, which asserts the opposite.
Indicates that the structures either side of it are contributing forms of one molecule, none of which exists on its own.
Contexts: Laboratory
Means the opposite of an equilibrium arrow, and the two are confused constantly. Equilibrium asserts two real species interconverting; resonance asserts one species that no single drawing captures.
Contexts: Laboratory
A single straight horizontal line with a full arrowhead at each end, drawn between two structural formulae.
Both are double-headed arrows between two expressions, in unrelated fields.
Opposite assertions made by similar-looking arrows.