CONCLUSION
The density functional theory (DFT) calculations showed that the keto tautomer is more stable than the enol
tautomers (Z&E) in the gas phase, while enol (Z) isomer is more stable than enol (E) isomer. The order of the dipole
movements for isomers are Keto > enol (Z) > enol (E). It can be seen that the ΔG values for the indicate that the
reaction is nonspontaneous and more stable form is enol(Z) isomer, which explain, intramolecular H-bonding is
between O8-H17 donor and N11 acceptor of the enol(Z) isomer, but in case of the enol(E) no intramolecular
hydrogen bond generate.