Structure and vibrational assignment of tautomerism of 4-hydroxyquinazoline in gaseous and aqueous phases

► The most stable tautomer of 4-HQ, in both of gas phase and water is 4-HQ1. ► Passing from gas phase to water changes the order of stability of tautomers. ► The dipole moments significantly relate to the nature of tautomers. ► The υ(CO), υ(NH) and υ(CH) modes are affected on going from gas phase to water.