Term: spin density
https://doi.org/10.1351/goldbook.S05864

Definition:
The unpaired electron density at a position of interest, usually at carbon, in a radical. It is often measured experimentally by electron paramagnetic resonance [EPR, ESR (electron spin resonance)] spectroscopy through hyperfine coupling constants of the atom or an attached hydrogen.

Related Terms:
1) radical centre (http://doi.org/10.1351/goldbook.R05069).
2) electron density (http://doi.org/10.1351/goldbook.E01986).
3) radical (http://doi.org/10.1351/goldbook.R05066).
4) paramagnetic (http://doi.org/10.1351/goldbook.P04404).
5) resonance (http://doi.org/10.1351/goldbook.R05326).
6) spectroscopy (http://doi.org/10.1351/goldbook.S05848).
7) hyperfine coupling (http://doi.org/10.1351/goldbook.HT07052).

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1166 (https://doi.org/10.1351/pac199466051077)

Citation: 'spin density' 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.S05864

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