Analysis of Radicals byEPR

AbstractThis article explains why electron paramagnetic resonance (EPR) spectroscopy is one of the most versatile and useful techniques for investigating free radicals. Easy to use EPR tools are expounded for organic chemists to exploit in researching the structures and reactivities of radicals and as a resource for synthetic planning. The article provides key references and introduces the literature on the EPR spectra of a wide range of organic radicals in solution. How EPR spectra result from molecules containing one unpaired electron (UPE) is explained and basic theory is presented for isotropic conditions. A correlation chart enablesg‐factors, which are key spectral parameters, to be used in determining which element is the principal site of the UPE. Methods of analysing complex EPR spectra and obtaining hyperfine splittings (hfs) are described. How geometries around the central atoms of radicals, and conformations about neighboring bonds, can be deduced from EPR data is explained. Modernab initiomethods of computing EPR parameters are briefly sketched. Features of the EPR spectra of model radicals centered on elements from groups 13, 14, 15, and 16 of the periodic table are surveyed. EPR methods for concentration measurements and for studying radical kinetics in time‐resolved and steady‐state modes are set out. Derivations from EPR spectral data of thermodynamic parameters such as radical enthalpies of formation and bond dissociation enthalpies are also explained.