Zeinab dalir nasab - Department of chem istry, university of arak. Arak Iran.Payamnoor university. Jahroom.Iran.
Ali Reza karim i - Department of chem istry, university of arak. Arak Iran.
Sudabeh dalirnasab - Depart ment of chemis try, university of shiraz. Shiraz Iran.
Abbas Ali Nikseresht - department of Nasb niro o company.

The c hemical pro perties of ۴- Hydroxycoumarin derivatives have been extensi vely studied . The re lative stability of three tautomers in the gas phase and solution (using PCM model) are evalua ted by usin g DFT method. The variation of dip ole moment s and charges on atoms with change of solvent is also studied.

Tauto merism, ۴- Hydroxycoumarin, DFT, PCM, NBO