Correlation of Electron-Transfer Rate Constants of Carbinons with Their Oxidation Potentials and Basicities

Article abstract of DOI:10.1021/ja00268a042

Acidity-oxidation-potential (AOP) values for seven 9-substituted fluorenide ions, 9-ArFl(1-), relative to that of fluorene, have revealed the presence of small radical-stabilizing effects for 4-MeO and 4-Me substitutents in the aryl ring and a 3-Me substituent in the fluorene ring and their absence for 3-Cl and 4-MeSO2 substituents in the aryl ring and 2-Br and 2-PhSO2 substituents in the fluorene ring.Measurements of redox potentials have shown that electron-transfer (e_T(1-)) reactions of these 9-ArFl(1-) ions with 1,1-dinitrocyclohexane are endergonic by 6.6-13 kcal/mol.A Bronsted-type plot of log k_obsd for these reactions vs. pK_HA was linear with scatter.A Bronsted-type plot of log k_obsd vs.E_ox gave an improved plot (β = 1.04; R² = 0.999) that covered a rate range of >1E5 and an E_ox range of 7.3 kcal/mol.Mechanistic schemes are presented to account for the products formed in the e_T(1-) reaction and to reconcile the strict linearity of the latter plot with the Marcus equation.