Determination of the substituent effect on the O-H bond dissociation enthalpies of phenolic antioxidants by the EPR radical equilibration technique

Giovanni Brigati; Marco Lucarini; Veronica Mugnaini; Gian Franco Pedulli

doi:10.1021/jo025755y

Determination of the substituent effect on the O-H bond dissociation enthalpies of phenolic antioxidants by the EPR radical equilibration technique

J Org Chem. 2002 Jul 12;67(14):4828-32. doi: 10.1021/jo025755y.

Authors

Giovanni Brigati¹, Marco Lucarini, Veronica Mugnaini, Gian Franco Pedulli

Affiliation

¹ Dipartimento di Chimica Organica A. Mangini, Università di Bologna, Via S. Donato 15, I-40127 Bologna, Italy.

PMID: 12098294
DOI: 10.1021/jo025755y

Abstract

The bond dissociation enthalpies (BDE) of several phenols containing electron-withdrawing substituents in the para position have been determined by means of the EPR radical equilibration technique. It has been found that CN, NO(2), CHO, COOR, and COOH induce an increase of the BDE value of the O-H bond, thus producing a worsening of the antioxidant activity of phenols, while Cl, Ph, and CH[double bond]CHPh show an opposite effect. The contributions of these substituents for the calculation of the BDE values in polysubstituted phenols by using the group additivity rule have also been derived. It is shown that this rule provides quite reliable predictions of bond strengths, so that the method can be conveniently used to estimate new data on substituted phenols.