Name: Electron Paramagnetic Resonance EPR Spectroscopy: Organic Radicals
Uploaded: 2023-04-30T11:20:07
Description: Learn by watching this video about Electron Paramagnetic Resonance EPR Spectroscopy: Organic Radicals at JoVE.com

A free unpaired electron would ideally lead to a single peak in the EPR spectrum resulting from the transition between two spin energy states.
However, in the presence of neighboring spin-active nuclei, the spectrum shows hyperfine splitting due to coupling between the electronic spin and nuclear spin.
The number of peaks obtained is given by 2nI + 1, where n is the number of equivalent nuclei present, and I, corresponds to the nuclear spin.
Thus, a methyl radical bearing three spin-active nuclei shows four peaks in the EPR spectrum&#8212;a quartet pattern&#8212;with relative peak intensities of 1:3:3:1.
In the case of a 1,4-benzosemiquinone radical, as the unpaired electron is delocalized over the ring, it exhibits hyperfine coupling with the ring hydrogen atoms, resulting in five peaks.&#160;
In EPR spectroscopy, the coupling intensity&#8212;known as the hyperfine splitting constant&#8212;is measured in millitesla or gauss units.
The magnitude of the splitting constant indicates the geometry of various radicals.

electron paramagnetic resonance (epr) spectroscopy: organic radicals

Ideally, an unpaired electron shows a single peak in the EPR spectrum due to the transition between the two spin energy states. However, coupling interactions can occur between the spins of the unpaired electron and any neighboring spin-active nuclei. This hyperfine coupling results in hyperfine splitting, where the EPR signal is split into multiplets. The signals split into 2nI + 1 peaks, where n is the number of equivalent nuclei and I is the nuclear spin. These splitting patterns provide valuable information about the radical. In a methyl radical, for example, the electron spin is coupled with the three spin-active hydrogen nuclei. The EPR spectrum shows four peaks (quartet) with relative peak intensities in the ratio of 1:3:3:1.
In the case of the 1,4-benzosemiquinone radical, the unpaired electron is delocalized over the ring and oxygen atoms making all protons equivalent. The electron is coupled with the four equivalent protons, splitting the signal into five peaks with relative peak intensities in the ratio of 1:4:6:4:1. The distance between the peaks is the hyperfine coupling constant, which is measured in gauss or millitesla units. The magnitude of the coupling constant indicates the geometry of various radicals.&#160;

Learn by watching this video about Electron Paramagnetic Resonance EPR Spectroscopy: Organic Radicals at JoVE.com