Photo-induced isomerization of three nitrotoluene isomers: A matrix-isolation infrared spectroscopic and quantum-chemical study

Abstract The photo-induced isomerization reactions of ortho -, meta - and para -nitrotoluene molecules were investigated by matrix isolation infrared spectroscopy and quantum chemical calculations. Under UV irradiation of ortho -nitrotoluene in solid argon, the hydrogen atom transfer isomer was formed, as reported previously. It was found that the hydrogen atom transfer isomer is unstable and rearranged to its nitro isomer upon annealing. In addition, the nitrite isomer as well as its dissociation product tolyloxy radical was also formed. Only the nitrite isomers and the tolyloxy radicals were formed upon UV excitation of the meta- and para -nitrotoluene molecules. Infrared spectra and vibrational frequency assignments of the newly observed nitrite isomers and tolyloxy radicals are reported, which are supported by quantum chemical calculations.