## 3 Results  
### Amines  
The mono-substituted N-alkylamines were treated earlier [1], and in that work, we established a NH\({}_{2}\)- amine Group Contribution parameter value of +13 kJ/mol. The averaged absolute difference between the experimental values and those of our GC model was found to be 1.20 kJ/mol (Table S15 in the Supplementary Materials). Referring to what we discussed above, it would be more appropriate to exclusively use reliable verified experimental data. When we disregard the entries for which we had data from the CAPEC database [32] (the explicit values were not published and therefore not quoted in this paper explicitly), we end up with Table 1. The entries in Table 1 originate either from [PERSON] [33], [PERSON] et al. [34], or [PERSON] et al. [35]. Compared to the larger set in Ref. [1], the averaged absolute deviation drops from 1.20 kJ/mol to 0.71 kJ/mol, with the annotation that methylamine was excluded. Firstly, this illustrates what we discussed before about the quality of experimental data and illustrates the better data selection. Secondly, for methylamine, the presence of the methyl Group to the nitrogen cannot be described appropriately, i.e., within chemical accuracy, by the GC model. We will observe this more often in cases to be discussed in subsequent sections, and therefore methyl-substituted nitrogen species should be considered separately. When we consider the G4 quantum results, these are, considering error bars, all within chemical accuracy, including methylamine, which confirms that G4 results are in good agreement with experimental values. Now, considering the 2-aminoalkanes, viz. Table 2, using the GC parameter for the NH\({}_{2}\) group, the heats of formation of isobutylamine and isobutylamine differ from their experimental values clearly beyond 4 kJ/mol, chemical accuracy. However, when we introduce an additional GC parameter associated with an NH\({}_{2}\) group in R-CH(NH\({}_{2}\))-R' and a numerical value of +3 kJ/mol, we obtain the results shown as the first two entries in Table 2, revealing agreement with experimental values within chemical accuracy. We will later see two more examples for which the introduction of this GC parameter leads to good agreement between experiment and model. As can be corroborated from Table 2, these results also agree very well with the G4 results. Next, we consider the symmetrical di-alkyl-substituted secondary amines R\({}_{2}\)NH\({}_{2}\). Experimental data and model values are collected in Table 3 along with the G4 quantum results. We needed, as expected based on what we saw before, to introduce another GC parameter for the secondary amine R-NH-R', and established a value of +51 kJ/mol to obtain good agreement between experimental and model values for four of the species \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**n-Alkylamines** & **Exp.** & **Model** & **Model – Exp.** & **ABS (Model – Exp.)** & **G4** & **G4 Avgd.** & **ABS (G4 Avgd. – Exp.)** \\ \hline methylamine & \(-23.0\) & \(-29.4\) & \(-6.4\) & \(6.4\) & \(-19.7\) & \(-19.7\) & \(3.3\) \\ \hline ethylamine & \(-48.6\) & \(-50.0\) & \(-1.4\) & \(1.4\) & \(-47.9\) & \(-47.8\) & \(0.8\) \\ \hline propylamine & \(-70.2\) & \(-70.6\) & \(-0.4\) & \(0.4\) & \(-68.3\) & \(-67.8\) & \(2.4\) \\ \hline butylamine & \(-92.0\) & \(-91.3\) & \(0.8\) & \(0.8\) & \(-89.0\) & \(-87.7\) & \(4.3\) \\ \hline octylamine & \(-173.5\) & \(-173.8\) & \(1\)-\(0.3\) & \(0.3\) & \(-174.3\) & \(-171.3\) & \(2.2\) \\ \hline averaged absolute difference & & & & \(0.7\) & & & \(2.4\) \\ \hline \end{tabular}
\end{table} 
Table 1: Experimental and model values for the primary amines. All values in kJ/mol. The difference between model and experimental data are based on the Rossini value for ethylamine [33] (p. 623); values for methylamine, propylamine and butylamine are from [PERSON] c.s. [34], and octylamine from [PERSON] et al. [35]. The averaged absolute difference is 0.71 kJ/mol without taking into account methylamine; for an explanation, see text.