The effect of Hg(II) ions on the free radicals of humic substances and their model compounds

► Hg(II) ions create new radical species in humic acids. ► Hydroxybenzenes and their benzoic acids are good models of humic acids radical centers. ► Formed complexes Hg(II) - semiquinone radicals are characterized by very low g-factor. ► Only ortho positioning of OH results in low g-factor radical complexes formation.