The use of electron spin resonance to measure reaction rates

At Cardiff, we have used electron spin resonance measurements to study the reactions of radical anions formed by the addition of electrons to unsaturated molecules. In certain cases the unsaturated molecule is such that the radical anion formed by the addition of the electron undergoes no reaction except that of disproportionation. For example, when the radical anion of tetraphenylethylene is made in tetrahydrofuran as solvent, disproportionation occurs: 2( Ph 2 C = C Ph 2 )· - Na + ⇌ Ph 2 C̅—C̅ Ph 2 + Ph 2 C = C Ph 2 . Na + Na + The presence of the four phenyl groups prevents the radical anion from dimerizing and electron transfer from one radical anion to another is the only possible reaction (Bennett, Evans, Evans, Owen & Tabner 1963; Evans & Evans 1963; Evans & Tabner 1963). In other cases, the radical anion formed by electron addition undergoes reaction and this reaction can be studied by the change with time of the electron spin resonance signal.