Radical anions of nitrobenzene on MgO and Al2O3, as investigated by electron spin resonance and electron nuclear double resonance spectroscopies

Abstract

Radical anions formed upon adsorption of nitrobenzene at room temperature on the surface of MgO and γ-Al₂O₃, previously activated by heating under vacuum, have been characterized by means of proton ENDOR and ESR spectroscopies. Fully deuterated nitrobenzene and oxides whose surface protons were exchanged with deuterons have been used in addition to non-deuterated products. On MgO, ESR experiments with deuterated nitrobenzene showed the presence of two radical species whose relative concentration depends strongly on the activation temperature of the oxide (673–1173 K). Hyperfine interactions with ring protons (ortho, meta and para) of the radical anion were resolved in the ENDOR spectra. Calculated spectra fitted the experimental ones well. Weak interactions of the radical with distant surface protons were observed, and surface protons of hydroxyl groups of γ-Al₂O₃, but not those of MgO, were observed to exchange with aromatic protons of the radical.