Chemical Physics, Physical Chemistry
Formazan and 3-nitroformazan have been investigated at abinitio level (MP2/6-31G** and B3LYP/6-31G**) in all their possible conformations, for studying the various possibilities of intramolecular hydrogen bonding formation. The trans-syn-s-cis (TSSC), known also asyellowform, has been found to be the most stable conformer (at least in the gas phase) in both compounds. This particular structure is strongly stabilized by a N–H···N hydrogen bridge, which gives rise to a hexatomic chelate ring, with the possibility of a proton transfer process.This closely resembles that of malondialdehyde, previously studied, in the evolution of the potential energy shape but with a greater barrier height. Various approaches for obtaining a quantitative estimate of the energy of the hydrogen bridges are discussed. The electronic structures of the most favoured TSSC, TSST (trans-syn-s-trans) and TAST (trans-anti-s-trans) conformations of formazan have been compared with those of the corresponding forms of 1,5-diphenylformazan, in order to account for the UV spectra available in the literature and the different colours exhibited by the molecule on passing from one conformation to another.
Published in Journal of the Chemical Society, Faraday Transactions, Volume 94, Issue 22, 1998, pages 3313-3319.
© Journal of the Chemical Society, Faraday Transactions 1998, Royal Society of Chemistry
Buemi, G., Zuccarello, F., Venuvanalingam, P., Ramalingam, M., & Ammal, S. S. C. (1998). Ab initio study of formazan and 3-nitroformazan. Journal of the Chemical Society, Faraday Transactions, 94(22), 3313-3319.