Bond dissociation enthalpies of polyphenols: the importance of cooperative effects.

The hydrogen-oxygen bond dissociation energies of 3,5-di-tert-butylcatechol, 2,5-di-tert-pentylhydroquinone, propyl gallate, and octyl gallate, which represent model compounds of three important classes of naturally occurring antioxidants, have been measured by an EPR equilibration technique, and the factors determining their values have been clarified. The excellent antioxidant activity of the these polyphenols is largely due to the stabilization of the aroxyl radical due to the formation of an intramolecular hydrogen bond.