Application of Optically Detected EPR to Study the Stability of Sterically Hindered Amine Radical Cations to Proton Transfer Reaction

Optically detected electron paramagnetic resonance technique has been applied to study the stability of sterically hindered amine radical cations with respect to the ion–molecule proton transfer reaction in liquid squalane solutions. The reaction has proved very sensitive to the steric effect of bulky tertiary substituents at the nitrogen atom. It has been established that steric hindrance is able to efficiently block the N–H proton transfer reaction, while the H-bonding may stabilize the distonic intermediate complex of aminyl radical and cation of ammonium type.