121619-87-2Relevant academic research and scientific papers
Use of the Hammett Correlation and ?+ for Calculation of One-Electron Redox Potentials of Antioxidants
Jovanovic, Slobodan V.,Tosic, Mihajilo,Simic, Michael G.
, p. 10824 - 10827 (2007/10/02)
Spectral, acid-base, and redox properties of methoxyphenoxyl radicals were determined in aqueous solutions by pulse radiolysis.Except for 2,6-dimethoxyphenoxyl, with λmax 7 = 0.58 V vs NHE, whereas the effect of meta substitution was minimal for 3,5-dimethoxyphenol, E7 = 0.85 V, yet this was 0.12 V lower than the measured E7 of 0.97 V for unsubstituted phenol.The reduction potential E7 of methoxyphenoxyl radicals satisfies the Hammett correlation using Brown ?+ substituent constants, as do other monosubstituted phenoxyls if the additivity of ?+ values is assumed and the state of protonation of the substituents is taken into consideration.The derived ?+(CH3O)m value of -0.14, in contrast to reported positive values, indicates the contribution of the methoxy group, even in the meta position, to charge delocalization and resonant stabilization of the phenoxyl radical.The contribution of the ring structure to more negative ?+ values was observed, as expected.Use of the Hammett correlation is suggested for rapid estimation and accurate calculation of the redox potentials of polysubstituted phenolic antioxidants.
