Resonance arrow

A double-headed straight arrow between two drawn structures.

Also known as: Double-headed arrow, Resonance

ScientificStandard profile

Meanings

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.

Common modern usageVerified fact
Indicates that the structures either side of it are contributing forms of one molecule, none of which exists on its own.
Contexts: Laboratory
Common modern usageVerified fact
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

Visual description

A single straight horizontal line with a full arrowhead at each end, drawn between two structural formulae.

Symmetry: point
Orientation: upright

Commonly confused with: If-and-only-if sign
Both are double-headed arrows between two expressions, in unrelated fields.
Commonly confused with: Equilibrium arrow
Opposite assertions made by similar-looking arrows.

Confidence

IdentityHigh confidence: High confidence because the identity is documented in encyclopedic references, but multiple independent sources agree.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but multiple independent sources agree, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is documented in encyclopedic references, but multiple independent sources agree.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references, but multiple independent sources agree.

Sources

Resonance (chemistry)
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol denotes in ordinary scientific practice and for which fields reuse it, never for a claim that any body assigns the letter its meaning.
IUPAC Compendium of Chemical Terminology (the Gold Book)
International Union of Pure and Applied Chemistry · retrieved 2026-08-01
The chemical community's own terminology reference, freely available. Cited for definitions of chemical terms and conventions; it does not govern how a reaction is drawn on a whiteboard, and records about drawing practice cite reference works instead.
Chemical equilibrium
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol denotes in ordinary scientific practice and for which fields reuse it, never for a claim that any body assigns the letter its meaning.

Last reviewed 2026-07-31

Part of

Chemical equation and structure notation

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Meanings

Common modern usageVerified fact

Indicates that the structures either side of it are contributing forms of one molecule, none of which exists on its own.

Contexts: Laboratory

Common modern usageVerified fact

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

Confidence

IdentityHigh confidence: High confidence because the identity is documented in encyclopedic references, but multiple independent sources agree.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but multiple independent sources agree, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is documented in encyclopedic references, but multiple independent sources agree.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references, but multiple independent sources agree.

Sources

Resonance (chemistry)
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol denotes in ordinary scientific practice and for which fields reuse it, never for a claim that any body assigns the letter its meaning.
IUPAC Compendium of Chemical Terminology (the Gold Book)
International Union of Pure and Applied Chemistry · retrieved 2026-08-01
The chemical community's own terminology reference, freely available. Cited for definitions of chemical terms and conventions; it does not govern how a reaction is drawn on a whiteboard, and records about drawing practice cite reference works instead.
Chemical equilibrium
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol denotes in ordinary scientific practice and for which fields reuse it, never for a claim that any body assigns the letter its meaning.

Last reviewed 2026-07-31

Meanings

Visual description

Related & commonly confused symbols

Meanings

Visual description

Related & commonly confused symbols