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 various tautomers of 6-flourothymine (FT). FT can be presentedby five tautomeric forms. All tautomers from 1, 3 hydrogen migration between N and O werein gas phas and Methanol solvent. And also by using frequency calculation at the same levelthermodynamic properties such as E, H, G and equilibrium constant (Keq) for fivetautomerism reactions were determined. Studies of tautomerism phenomena have beenvaluable in many areas of chemistry a demonstrated by several reviews. [1,2,3,4]. In thepresent work, From the calculations, relative energies and thermodynamic properties oftautomerism equilibrium in FT were obtained. Thence, the effects of solvent on theequilibrium have been investigated using Methanol as solvent and gas phase.