Spektroskopische Untersuchungen über die Rolle des Käfig‐Effektes bei der Prädissoziation aromatischer Nitroverbindungen

Photolysis of the bond Rar–NO2 contributes to quenching of the fluorescence of aromatic nitro compounds. Since no nitro compound is known which fluoresces above 20,000 cm−1 photolysis must occur via a predissociation process. Either a fluorine‐substituted nitro compound or fluorobenzene as the solvent was used for the irradiation experiments so that 19F‐NMR. spectroscopy could be used to analyse the reaction products. Cage effects play an important role. With a large distance between the radicals Rar and NO2, the phenyl radical forms a diphenyl compound with a benzenetype solvent molecule, and with small distance recombination will occur. For medium to long distances geminal recombination will also occur, not to the initial nitro compound, but to the corresponding nitrite, which in the presence of oxygen forms o‐nitrophenol. Mass spectrometry showed that the added oxygen atom is located in the nitro group.