## 3 Results
### Amines

Table 4: Experimental, present GC model, and G4 model values for the heat of formation for some symmetrical tri-alkylamines R\({}_{3}\)N. Experimental values taken from (i) trimethylamine Cox and Pilcher [38] and (ii) triethyl- and tripropylamine: Pedley c.s. [34]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Various Secondary and** & **Exp.** & **Model** & **Model – Exp.** & **G4** & **G4 Avgd.** & **G4 Avgd. – Exp.** \\ \hline butylisobutylamine & \(-171.0\) & \(-163.7\) & \(7.3\) & \(-164.6\) & \(-161.8\) & \(9.2\) \\ \hline N-methyl-butanamine & \(-108.3\) & \(-94.6\) & \(13.7\) & \(-85.8\) & \(-83.6\) & \(24.7\) \\ \hline N,N-dimethyloctylamine & \(-178.9\) & \(-179.0\) & \(-0.1\) & \(-177.2\) & \(-174.2\) & \(4.7\) \\ \hline terbutylmethylamine & \(-110.0\) & \(-124.7\) & \(-14.7\) & \(-109.0\) & \(-109.0\) & \(1.0\) \\ \hline terbutylisopropylamine & \(-168.1\) & \(-173.2\) & \(-5.1\) & \(-166.3\) & \(-165.3\) & \(2.8\) \\ \hline N,N-dimethylbutan-1-amine & \(-96.5\) & & & \(-92.4\) & \(-91.1\) & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Experimental, present GC model, and G4 model values for the heat of formation for a number of non-symmetrical secondary and tertiary amines of the types RR\({}^{\prime}\)NH and RR\({}^{\prime}\)R\({}^{\prime\prime}\)N. Values in kJ/mol. Entry 1 from [PERSON] c.s. [34], entry 2 from [PERSON] c.s. [39], and entries 3–5 from [PERSON] [40]. The G4 averaged value for N,N-dimethyloctylamine is an estimate based on the minimum energy conformer (\(-174.3\) kJ/mol) and a correction of 3 kJ/mol for the effect of the conformers (estimate based on the numerical values for shorter alkyl chains). the agreement between the GC and G4 values is not much beyond chemical accuracy (5.5 kJ/mol). A preliminary conclusion is that N,N-dimethylamine does not reveal a larger deviation. _Tert_-butylisopropylamine shows a deviation slightly beyond chemical accuracy, but considering the error in the experimental value of 3.2 kJ/mol as provided by [PERSON] c.s. [40], the GC model is considered to perform well enough. In Table 6, we collect data for diamines. For all three species with a 1,2-diamine, we need two different amine parameters, as determined before (see above) for N-alkyl amines and 2-aminoalkanes, respectively. The resulting GC values for the heat of formation agree with the experimental values within chemical accuracy, as do the G4 results. In summary, for the amines, we generally observed good agreement between our GC model and the experimental values. In a few cases, for which the difference was somewhat beyond chemical accuracy, the error in the experimental data can account for this, and therefore the GC model values are considered acceptable for a model aiming for chemical accuracy. The general exception for good agreement within chemical accuracy are those species that have a methyl Group attached to the amine nitrogen. These include methylamine (\(-\)6.4 kJ/mol), dimethylamine (\(-\)14.1 kJ/mol), trimethylamine (\(-\)10.9 kJ/mol), N-methyl-buttanamine (\(-\)8.8 kJ/mol when compared to the G4 result), and _tert_-butylmethylamine (\(-\)14.7 kJ/mol). From a pragmatic point of view, when adding +11 kJ/mol to all methyl-substituted species, we have agreement between experimental and GC values and almost chemical accuracy for all five named species. A preliminary conclusion is that this larger deviation for methylamines does not apply to N,N-dimethylamines, but further data are required to confirm this. A better way, when the expertise and methodology are available, is to obtain the heat of formation for such species from G4 calculations.