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

Abstract

Gas-phase enthalpies of formation of 122 relatively large organic molecules with up to 15 non-hydrogen atoms have been calculated at the Gaussian-4 (G4

Enthalpy of formation of guanidine and its amino and nitro derivatives

“…Figure 3 shows that the G4 calculation applied to atomization reaction overestimates the enthalpy of formation of guanidine; the addition of one or two NH 2 groups has a small influence on the D f H 298 (g) value, while that of three amino groups increases the overestimation effect. Earlier it was found that G4 theory underestimates the D f H 298 (g) values for nitro compounds [22,23]. The same trend, as can be seen from Fig.…”

“…The same trend, as can be seen from Fig. 3, is also observed for nitroguanidines; however, the presence of guanidine fragment decreases this underestimation somewhat compared to aliphatic and aromatic nitro compounds [22,23]. The largest underestimation is observed for dinitroguanidines; the addition of NH 2 groups somewhat compensates for the effect of NO 2 groups.…”

“…The G4 method was found to be accurate in calculating the enthalpies of formations of different classes of compounds. However, as it was found in our previous works [22,23], the G4 theory underestimates the D f H 298 values of the most nitro compounds by up to 20 kJ/mol. A good agreement with experiment was obtained only when the isodesmic reactions were used instead of the atomization reaction.…”

Experimental and theoretical study of thermodynamic properties of levoglucosan

“…If the latter value is corrected for the enthalpy of mixing of the conformers equal to 4.5 kJÁmol -1 at 15 K) = À836.0 kJ Á mol À1 agrees satisfactorily with the experimental value. Dorofeeva et al [32,33] noted that the G4 method produces too negative D f H o m values for heterocyclic oxygen compounds if the atomization scheme is used. The reason why the use of isodesmic reactions does not improve convergence with the experimental value is unknown.…”

Ga+Basicity and Affinity Scales Based on High‐Level Ab Initio Calculations

“…[13] Furthermore, very recently it has been shown to be well suited to reproduce experimental AlCAs and AlCBs. [1m] This method introduces several improvements with respect to previous methods of the same series, namely,t he geometry optimization procedure, as well as the calculation of thermal corrections, is carried out at the B3LYP/6-31G(2df,p) level, an estimation of the Hartree-Fock energy limit is included in the calculation of the final energies, as well as two high-level empirical corrections.…”