Calculation of the enthalpies of formation and proton affinities of some isoquinoline derivatives

Mansoor Namazian, Michelle L. Coote

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14 Citations (Scopus)


Ab initio molecular orbital theory has been used to calculate enthalpies of formation of isoquinoline, 1-hydroxyisoquinoline, 5-hydroxyisoquinoline, and 1,5-dihydroxyisoquinoline as well as some pyridine and quinoline derivatives. The proton affinities of the four isoquinoline derivatives were also obtained. The high-level composite methods G3(MP2), G3(MP2)//B3LYP, G3//B3LYP, and CBS-QB3 have been used for this study, and the results have been compared with available experimental values. For six of the eight studied compounds, the theoretical enthalpies of formation were very close to the experimental values (to within 4.3 kJ · mol-1); where comparison was possible, the theoretical and experimental proton affinities were also in excellent agreement with one another. However, there is an extraordinary discrepancy between theory and experiment for the enthalpies of formation of 1-hydroxyisoquinoline and 1,5-dihydroxyisoquinoline, suggesting that the experimental values for these two compounds should perhaps be re-examined. We also show that popular low cost computational methods such as B3LYP and MP2 show very large deviations from the benchmark values.

Original languageEnglish
Pages (from-to)1627-1631
Number of pages5
JournalJournal of Chemical Thermodynamics
Issue number12
Publication statusPublished - Dec 2008
Externally publishedYes


  • Enthalpy of formation
  • G3
  • Isoquinoline
  • Proton affinity


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