Electron Paramagnetic Resonance Spectroscopy in Radical Chemistry
Summary
Electron Paramagnetic Resonance (EPR) spectroscopy is a powerful tool for probing unpaired electrons in radical species, providing detailed insight into electronic structure, dynamics and interactions with surrounding nuclei. In radical chemistry, EPR enables the characterisation of both transient intermediates and stable paramagnetic species, revealing key parameters such as g tensors and hyperfine coupling constants. These parameters elucidate the spatial distribution of spin density and its modulation by molecular geometry, solvation and external fields. Recent advances in instrumentation—specifically multi-frequency and high-field EPR—and computational methodologies have refined the accuracy of spectral simulations and property predictions, bridging experiment with theory. The technique finds global application in fields as diverse as materials science, catalysis and biophysics, where radical intermediates underpin processes ranging from polymerisation to enzymatic redox reactions. By combining EPR with ab initio molecular dynamics, density functional theory and machine learning, researchers now map radical reactivity pathways and solvent effects with unprecedented precision, catalysing new discoveries in radical design, antioxidant development and spin-based sensing technologies.
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Electron Paramagnetic Resonance Spectroscopy in Radical Chemistry publication trend
The graph below shows the total number of articles in electron paramagnetic resonance spectroscopy in radical chemistry across all publications each year (not limited to Nature Index journals).
Technical terms
Electron Paramagnetic Resonance (EPR) spectroscopy: A magnetic resonance technique that detects transitions of unpaired electron spins in paramagnetic species under applied magnetic fields.
Radical: A molecule or ion containing at least one unpaired electron, often highly reactive and central to redox processes.
Hyperfine coupling constant: A parameter quantifying the interaction strength between unpaired electron spins and nearby nuclear spins, observable as splitting in EPR spectra.
g tensor: A three-component tensor describing the anisotropy of the electron Zeeman interaction; deviations from the free-electron g value reflect electronic environment.
Spin probe: A stable radical intentionally introduced into systems to report on local polarity, dynamics or molecular interactions via its EPR signature.
g strain: Variations in g-tensor values within an ensemble of radicals that lead to frequency-dependent broadening of EPR spectral lines.
References
- Gauging the importance of structural parameters for hyperfine coupling constants in organic radicals. RSC Advances (2023).
- Dissecting the Molecular Origin of g‑Tensor Heterogeneity and Strain in Nitroxide Radicals in Water: Electron Paramagnetic Resonance Experiment versus Theory. The Journal of Physical Chemistry A (2023).
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