IUPAC - resonance form (08205)

resonance form

Synonyms: canonical form, contributing structure, resonance structure

https://doi.org/10.1351/goldbook.08205

One of at least two Lewis structures, with fixed single, double, and triple bonds, that is a contributing structure to the valence-bond wavefunction of a molecule that cannot be described by a single Lewis structure.

Notes:

Although the valence-bond wavefunction is a linear combination of the wavefunctions of the individual resonance forms, the coefficients and the relative contributions of the various resonance forms are usually kept qualitative. For example, the major resonance forms for the conjugate base of acetone are $CH_{2} = C (CH_{3}) - O^{-}$ and $H_{2} C^{-} - C (CH_{3}) = O$ , with the former contributing more.
Resonance forms are connected by a double-headed arrow ( $\leftrightarrow$ ). This must not be confused with the double arrow connecting species in equilibrium ( $⇋$ ).

Source:
PAC, 2022, 94, 353. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 2021)) on page 499 [Terms] [Paper]

Citation: 'resonance form' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.08205 RIS BibTex EndNote

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resonance form