RADICAL-ANIONS OF DINITROPHENOLS IN AQUEOUS-SOLUTION - INTRAMOLECULARELECTRON-EXCHANGE AND ACID-BASE EQUILIBRIA

The radical-anions of three symmetrical dinitrophenols (3,5-dinitrophe nol, 2,6-dinitrophenol and 4,6-dinitrobenzene-1,3-diol) in aqueous sol ution have been studied by EPR spectroscopy in the range of pH values from 6.5 to 13. EPR spectra of radical-anions of 3,5- and 2,6-dinitrop henol show line-broadening effects due to intramolecular electron exch ange induced by asymmetric solvation of the two nitro groups. The posi tion of the OH group is a decisive factor in the variation of the rate constant with the deprotonation of the radical-anion. This variation is larger when the OH group is in the ortho position to one nitro grou p. The activation parameters for the intramolecular electron exchange reaction have been determined by using the Marcus theory and the Rips- Jortner equation for the rate constant of a uniform and adiabatic reac tion. Delta G values range from 12.6 kJ mol(-1) for radical-dianion o f 2,6-dinitrophenol to 46.0 kJ mol(-1) for radical-dianion of 3,5-dini trophenol. The EPR spectra of the radicals derived from 4,6-dinitroben zene-1,3-diol show no line-broadening effects in the experimental rang e of temperatures. In the radical-anion and radical-dianion, the elect ron is localised mainly in one nitro group, while in the radical-trian ion the spin density is evenly distributed over the two nitro groups. The pK(a) values of the radical-anions are in the range 8-11.