Assessment of Gaussian-4 theory for the computation of enthalpies of formation of large organic molecules

摘要: Gas-phase enthalpies of formation 122 relatively large organic molecules with up to 15 non-hydrogen atoms have been calculated at the Gaussian-4 (G4) level theory using atomization reaction procedure. The values were compared experimental data published mainly last years. Particular attention has given nitro compounds and nitrogen, oxygen, sulfur containing heterocyclic compounds. expected accumulation systematic errors as molecular size increases was not observed increasing number from 6 15. largest mean absolute deviation between G4 formation, 10.7 kJ/mol, revealed for All theoretical underestimated by 5–15 kJ/mol. best agreement experiment 4.5 kJ/mol which types widely presented in original test set method. deviations nitrogen heterocycles (6.8 kJ/mol) oxygen (9.1 are noticeably larger. Experimental four (N,N-dinitromethanamine, 2,3,5,6-tetrachloronitrobenzene, 2-methyl-2H-tetrazole, proline) suggested be unreliable comparison energies isodesmic reactions.