Behzad Chahkandi - Department of Chemistry,Islamic Azad University,Shahroodbranch,Shahrood,Iran
Alireza Yousenia - Department of Chemistry,Islamic Azad University,Shahroodbranch,Shahrood,Iran
Mehdi Nekoei - Department of Chemistry,Islamic Azad University,Shahroodbranch,Shahrood,Iran

1,2,4-Triazole and its derivatives represent one of the most biologically active classes ofcompounds, possessing a wide spectrum of activities. 3-amino-1H-1,2,4-triazole and itsderivatives have attracted much attention in the literature, particularly in the areas ofmedicinal and agrochemical research due to their biological activities. For example, 3-amino-1H-1,2,4triazoles are reported to inhibit catalase [1] and histidine biosynthesis [2], inhibitmethionine aminopeptidase-2 [3] and neuropeptide Y receptor [4], and act as histamine H2-receptor [5] and CRF1 receptor antagonists [6]. They also have shown various therapeuticapplications, such as anti-inflammatory and anti-asthmatic activities [7], and have beenstudied for the treatment of Alzheimer’s disease or Down syndrome [8].Determination of the structure and electron distribution of members of the aminoheterocyclicseries is thus important. Conceptual density functional theory (DFT) has been widely used tostudy the chemical reactivity and site selectivity of various molecular systems. The aim ofthis study is to investigate the tautomerism of one of the new derivatives of 1,2,4-Triazole.Despite the importance of tautomerism in triazoles, any reports about the study oftautomerism in 3-amino-1H-1,2,4-triazol-5(4H)-one (ATO) have not been observed in theliteratures. In the present work, a complete tautomeric scheme and the reaction paths betweensix tautomers of ATO (Fig. 1) were studied at the B3LYP/6-311++G(d,p) level of theory.