Low-temperature proton nuclear magnetic resonance and ultraviolet absorption spectra and photochemistry of the system nitrosobenzene–azodioxybenzene and its methyl derivatives

Abstract

The title compounds crystallize in their dimeric, azodioxy form, but their dilute solutions at room temperature contain only the monomeric, nitroso form. By dissolving the crystals at temperatures below –60 °C, dilute solutions of the dimers could be obtained, because thermal equilibration of the monomer and dimer no longer takes place at this temperature. The absorption spectra of the dimers, their dissociation kinetics at various temperatures above –60 °C, and their photochemistry in solution at and below –60 °C were thus investigated. The only photochemistry observed was a very efficient photo-dissociation of dimer to monomer, which takes place with close to unity yield even at –170 °C. The activation energies for the thermal dissociation of the dimers were found to be 80–100 kJ mol^–1.