Title: contributing structure
Long Title: IUPAC Gold Book - contributing structure
DOI: 10.1351/goldbook.C01309
Status: current

Definition
The definition is based on the valence-bond formulation of the quantum mechanical idea of the wavefunction of a molecule as composed of a linear combination of wavefunctions, each representative of a formula containing bonds that are only single, double or triple with a particular pairing of electron spins. Each such formula represents a contributing structure, also called 'resonance structure' to the total wavefunction, and the degree to which each contributes is indicated by the square of its coefficient in the linear combination. The contributing structures, also called 'canonical forms', themselves thus have a purely formal significance: they are the components from which wavefunctions can be built. Structures may be covalent (or non-polar) or ionic (or polar). The representation is frequently kept qualitative so that we speak of important or major contributing structures and minor contributing structures.

Example
The two major non-equivalent contributing structures for the conjugate base of acetone are: 

Related Terms
- Kekulé structure: https://goldbook.iupac.org/terms/view/K03373
- coefficient: https://goldbook.iupac.org/terms/view/C01124
- delocalization: https://goldbook.iupac.org/terms/view/D01583
- resonance: https://goldbook.iupac.org/terms/view/R05326
- valence: https://goldbook.iupac.org/terms/view/V06588

Source
- PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1100 (https://doi.org/10.1351/pac199466051077)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/C01309/html
- json: https://goldbook.iupac.org/terms/view/C01309/json
- xml: https://goldbook.iupac.org/terms/view/C01309/xml

Citation: Citation: 'contributing structure' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.C01309
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Accessed: 2026-06-28T13:28:12+00:00