Role of structure, medium and pathway in electrophilic aromatic substitutions. Part 3. Influence of isotope and solvent effects on electron release from phenolic O–H σ-bonds

Abstract

The rate of molecular bromination of phenol at 25 °C in CH₃CO₂¹H as solvent exceeds the rate of the corresponding reaction in CH₃CO₂²H by a factor of 1.5. Correction for substrate–solvent interaction brings the rate ratio to ca. 4.5, further confirmed by competitive bromination in the two media. A solvent isotope effect of this magnitude is indicative of substantial contribution to electrophilic reactivity from phenolic O–H σ-bonds.