Electron Spin Resonance of Radicals and Ions in Solution

Abstract

The electron spin resonance (ESR) also called electron paramagnetic resonance (EPR) spectroscopy offers the most favorable method for detection and characterization of radicals and paramagnetic ions. Due to its very high sensitivy and specificity this technique occupies a key position in the field of radical chemistry. The ESR method has the ability to detect unpaired electrons thus offering the possibility for a direct detection and identification of radicals. The fundamental limitations of this method are the chemical lifetime of the paramagnetic species which is determined by the steady state concentration controlled it self by the rate of production and disappearance of the species and the lifetime of the unpaired electron on its electronic levels which is reflected by the width of the ESR line. The purpose of this lecture is to discuss the way in which relevant informations about the structure of the radical, the nature of the unpaired electron orbital, the spin distribution along the molecule fragment are derived from an ESR experiment and how these experimental data can be related to the theoritical calculation of the electron distribution along the molecule. Furthermore an attempt will be made to provide relevant examples where the ESR method has been usefully employed for the benefit of the chemists.