The Role of Singlet and Triplet Dioxygen Molecules in the EPR and 1H NMR Spectrum Line Broadening

Abstract

In the Mo(VI)/H2O2/H2O system, the relaxation time (T 1) of protons in a water molecule and in a CH3 group decreases 10 to 30 times under conditions of dismutation of H2O2 with the formation of 1O2(1Δg). It is experimentally found that the overequilibrium concentration of triplet dioxygen cannot be the reason behind a decrease in T 1 in the 1H NMR spectra. Neither can it explain the anomalous line broadening in ESR spectra under conditions of 1O2(1Δg) formation in the systems V(V)/H2O2/AcOH and Mo(VI)/H2O2/H2O. Ab initio calculations showed that it is principle possible that the 3O4(3·- g-1Δg) molecule exists in a snake-like form and is formed by the reaction between 3O2(3·- g) and 1O2(1Δg), which is the product of H2O2 decomposition in the systems V(V)/H2O2/AcOH and Mo(IV)/H2O2/H2O. The interaction of 1O2 with the ·OOH radical is exothermic (ΔQ = 2.30 kcal/mol) and leads to the formation of ·OOOOH. It is assumed that the paramagnetic species of type ·OOOOH or 3O4(3 A 1) that is formed in the reaction might be responsible for the spectral effects observed.