DFT and ab initio Studies on Stability and Isomerization of Benzofuroxan

B3LYP/6-31G（d）-DFT （Density Functional Theory） method has been employed to study benzofuroxan,o-dinitrosobenzene and the isomerization between them. The calculated results with B3LYP/6-31G（d）-Dry show: （1） the molecular total energy of benzofuroxan is lower than that of o-dinitrosobenzene; （2） the activation energy （E_a⁺= 51.0 kJ/mol） of forward reaction that benzofuroxan isomerises into o-dinitrosobenzene, is in agreement with the experimental （58.6kJ/mol） provided by reference, and the activation energy （E_a^-=4.6kJ/mol） of backward reaction is very small. It is concluded thereby that beazofuroxan is more stable than o-dinitrosobenzene. In addition, the corresponding ah initio calculations at the level of HF/3 - 21G, HF/6 —31G（d） and MP2/6— 31G（d）//6 - 31G（d） were completed, and it was found that the calculable results by B3LYP-DFT method are superior to those from ab initio calculation. The calculations of harmonic vibrational frequencies with B3LYP/6-31G （d） theoretically supports that o-dinitrosobezene is the intermediate of "self-self" tautomeric rearrangement of benzofuroxan.