## 3 Results
### Amines
The G4 averaged value for octylamine 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). \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**2-Aminoalkanes** & **Exp.** & **Model** & **Model – Exp.** & **ABS (Model – Exp.)** & **G4** & **G4 Avgd.** & **ABS (G4 Avgd. – Exp.)** \\ \hline
2-butylamine & \(-104.9\) & \(-102.4\) & \(2.6\) & \(2.6\) & \(-104.0\) & \(-102.4\) & \(2.5\) \\ \hline Isopropylamine & \(-83.8\) & \(-85.7\) & \(-1.9\) & \(1.9\) & \(-83.9\) & \(-82.9\) & \(0.9\) \\ \hline Isobutylamine & \(-98.6\) & \(-98.5\) & \(0.2\) & \(0.2\) & \(-97.4\) & \(-96.9\) & \(1.7\) \\ \hline
2-propanamine, 2-methyl- = & \(-120.9\) & \(-121.4\) & \(-0.5\) & \(0.5\) & \(-121.3\) & \(-121.3\) & \(0.4\) \\ t-butylamine & & & & & & & \\ \hline averaged absolute difference & & & & \(1.3\) & & & \(1.4\) \\ \hline \end{tabular}
\end{table} 
Table 2: Experimental, present GC model, and G4 model values for the heat of formation for three primary alkyl amines. All values in kJ/mol. Experimental data from [PERSON] c.s. [34] except for isobutylamine [36]. in Table 3 (entries 2, 3, 4, and 7). Similar to the results for the primary alkyl amines, dimethylamine is an exception and should be treated separately rather than introducing additional parameters for a single species only, and as for methylamine, one can apply the G4 method to obtain a good value with chemical accuracy compared to the experimental value. The GC results for diisopropyl and diisobutylamine reveal a larger difference when compared to the experimental values. The G4 results (column 6 in Table 3) also reveal a difference of over 8 kJ/mol for diisopropylamine, all with reference to the experimental data from [PERSON] et al. (2014). There are also data due to [PERSON] c.s. (2016), and adopting their value for diisopropylamine reveals very good agreement with the [PERSON] averaged G4 result (difference 0.7 kJ/mol), whereas the GC value is off by 6.7 kJ/mol, which is considerably lower than when compared to [PERSON]'s data (over 14 kJ/mol) and not that much beyond chemical accuracy. As we overall get good results from our GC model and G4 generally provides values close to the experimental ones, we thus suspect that the experimental value for diisopropylamine from [PERSON] c.s. is insufficiently reliable. For diisobutylamine, the G4 results (conformationally averaged) are clearly significant deviating from the experimental values (7.9 and 9.5 kJ/mol for [PERSON]'s and [PERSON]'s experimental values, respectively). The presence of some steric hindrance is realistic for diisopropylamine and may account for the difference between the GC value and the experimental value, whereas the G4 and the experimental value ([PERSON] c.s.) agree very well. When we compare the experimental and model findings collected in Table 3, it remains elusive why both the GC and G4 values are 8-10 kJ/mol away from the experimental value for diisobutylamine, see Figure 1, as for this structure no steric effects are expected. The only potential reason seems to be a problem with the experimental value, as the G4 results are consistent throughout, and without any expected steric or electronic effects, in good agreement with the GC model. For the tertiary trialkylamines R3N, we observe very similar results, as shown in Table 4. Another GC parameter was introduced for the tertiary nitrogen with a value of +92.5 kJ/mol. All three G4 results agree very well with the experimental values. For the GC approach, once more the trimethylamine is the exception and should be treated as a  
Figure 1: Chemical structure of diisobutylamine.