Behzad Chahkandi - Department of Chemistry, Shahrood Branch, Islamic Azad University, Shahrood, Iran
Abdolreza Faramarzi Palangar - Department of Chemistry, Shahrood Branch, Islamic Azad University, Shahrood, Iran
Shima Khalilian - Department of Chemistry, Shahrood Branch, Islamic Azad University, Shahrood, Iran

Investigation of tautomerism and transition states in a derivative of 1,3,4-oxadiazole (A, B, C and D)in the gas phase was performed by calculations at the DFT-B3LYP/6-311++G(d,p) level oftheory. The geometries of four possible tautomers of 5-(x-amino)-1,3,4-oxadiazole-2(3H)-onewere optimized in the gas phase .It was found that in the gas phase , transition states C→D and A→D tautomers are the moststable and unstable forms, respectively. The results show that the tautomeric interconversionC→D has the lowest Gibbs free energy changes and so the highest equilibrium constant inthe gas phase . The calculated results show that the highest rate k forward in the transition statesC→D In the substituent F and lowest rate k forward in the transition states A→D In the substituentBr and highest rate k reverse in the transition states A→D In the substituent Br and lowest ratek reverse in the transition states C→D In the substituent F .

Oxadiazole, Tautomerism, Proton transfer, DFT calculations,Halogen