Spectroscopic and photochemical properties of mononitropyrenes

Article abstract of DOI:10.1002/recl.19871060403

The influence of the nitro group on the aromatic ?-system of pyrene has been studied by comparing the spectroscopic and photochemical properties of the three mononitropyrenes.Whereas the UV and mass spectra of 1- and 4-nitropyrene show an interaction normal for nitro-aromatic compounds, this is not observed for 2-nitropyrene.The lack of interaction is reflected in a UV spectrum very similar to that of pyrene and a mass spectrum with a very low abundance of M-NO.The photochemical behaviour of the three compounds is governed by the degree of interaction. 1-Nitropyrene shows the nitro-nitrite rearrangement leading to 1-hydroxypyrene (88percent) and 1-hydroxy-2-nitropyrene (7percent).The photoproducts of 4-nitropyrene are pyrene (9percent) and unstable products which react with the solvent. 2-Nitropyrene is very stable under photochemical conditions due to lack of interaction.Similarly, the sterically hindered 1-methyl-2-nitropyrene is also very stable towards light.The photochemical nitro-nitrite rearrangement observed for nitro-aromatic compounds was found to be governed by electronic effects.