The Electron Paramagnetic Resonance Spectra of α-Substituted Nitrotoluene Anion Radicals. The Influence of Electron-Withdrawing Substituents on the Coupling Constants for β-Hydrogen Atoms

We have obtained new experimental and theoretical information which indicates that electron-withdrawing substituents importantly diminish the magnitude of spin delocalization to β-hydrogen atoms in radicals. These substituent effects are so large that the EPR coupling constants for β-hydrogen atoms, a_β-H, cannot be used without correction to estimate conformational preferences, to detect structural changes such as bridging (distortion), or to guide the experimental assessment of β₂ parameters for other β-atoms, such as fluorine.