Behzad Chahkandi - Department of Chemistry , Shahrood Branch, Islamic Azad University, Shahrood, IRAN
Behzad Ajamian - South Pars Refinery, The first refinery, The operation, Bushehr, IRAN
Narges Bafekr Shirvan - Department of Chemistry , Shahrood Branch, Islamic Azad University, Shahrood, IRAN

Quantum calculations were carried out to determining structural parameters, energies andthermodynamic properties of transition state(TS) of various tautomers of 6-flourothymine(FT). FT can be presented by five TS forms. All TS from 1, 3 hydrogen migration between Nand O in Methanle solvent. And also by using frequency calculation at the same levelthermodynamic properties such as E++, H++, G++ and rates constant (Krat) for fivetautomerism reactions were determined. Studies of tautomerism phenomena have beenvaluable in many areas of chemistry a demonstrated by several reviews of experimental andtheoretical studies in chemistry and biochemistry. [1,2,3]. In the present work, a complete TSscheme for tautomers for FT (Fig. 1) were studied using B3LYP/6-311++G(d,p) level oftheory. In addition, From the calculations, thermodynamic properties of TS of tautomerismequilibrium in FT were obtained. Thence, the effects of solvent on the TS of equilibrium havebeen investigated using Methanole as solvent.