Namazian, MansoorCoote, Michelle2015-12-100021-9614http://hdl.handle.net/1885/57288Ab initio molecular orbital theory has been used to calculate enthalpies of formation of the keto tautomers of 1-hydroxyisoquinoline, 5-hydroxyisoquinoline, and 1,5-dihydroxyisoquinoline. The high-level composite method G3//B3LYP has been used for this study, and the results have been compared with available experimental values. The keto tautomer is more favourable for 1-hydroxyisoquinoline and 1,5-dihydroxyisoquinoline, and the experimental enthalpies of formation are in better agreement with the theoretical enthalpies of formation of the keto forms.Keywords: Ab initio molecular orbital theory; Composite method; Enthalpies of formation; Enthalpy of formation; Experimental values; G3; Isoquinoline; Isoquinolines; Tautomerism; Molecular orbitals; Proton transfer; Enthalpy Enthalpy of formation; G3; Isoquinoline; Tautomerism200910.1016/j.jct.2009.06.0272016-02-24