Term: spin label
https://doi.org/10.1351/goldbook.S05868

Definition:
A stable paramagnetic group (typically a nitryl radical) that is attached to a part of a molecular entity whose microscopic environment is of interest and may be revealed by the electron spin resonance (ESR) spectrum of the spin label. When a simple paramagnetic molecular entity is used in this way without covalent attachment to the molecular entity of interest it is frequently referred to as a 'spin probe'.

Related Terms:
1) stable (http://doi.org/10.1351/goldbook.S05900).
2) group (http://doi.org/10.1351/goldbook.G02705).
3) molecular entity (http://doi.org/10.1351/goldbook.M03986).
4) paramagnetic (http://doi.org/10.1351/goldbook.P04404).
5) resonance (http://doi.org/10.1351/goldbook.R05326).
6) label (http://doi.org/10.1351/goldbook.L03424).
7) attachment (http://doi.org/10.1351/goldbook.A00512).

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 label' 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.S05868

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