The Photochemical Dimerization of 4-Nitro-2-Phenylindone. A DFT Study

A DFT study of the photochemical dimerization on 4-nitro-2-phenylindone has been performed. The reaction was performed by Marussia Bakunin in 1911 but the reaction products were not identified. Calculations allow us to know that the reaction occurred through the first excited singlet state. The nature of the first excited singlet state allowed the formation of both head-to-head and head-to-tail dimers. Finally, the main product was the syn-trans head-to-tail dimer, while the other two compounds found by Bakunin in lower yields were the syn-trans head-to-head dimer and the syn-cis head-to-tail dimer. The results described by Bakunin can not be interpreted assuming the reaction occurred through the formation of the excited triplet state.