## 3 Results
### Substituted Benzenes
#### 3.3.2 Anilines  
Table 9 contains data on anilines. The GC model comprises the Group parameters as previously established for the various classes of amines. In addition, for the anilines with an alkyl substituent to the benzene ring, there is a substitution parameter involved, as we established for the alkyl substituted benzenes [1], 6 kJ/mol for single substitution and 18.5 kJ/mol for double substitution. In addition, we needed to introduce an additional interaction parameter of a magnitude of \(-\)7 kJ/mol for the NH\({}_{2}\)-benzene pair to obtain good agreement between experimental and GC model values. The agreement between experimental and GC model values is good, except for N,N-dimethylaniline. The G4 quantum values agree with the experimental values for all species including N,N-dimethylaniline, and, consequently, we conclude that there is a specific problem with the GC model for N,N-dimethylaniline. Although the difference is very similar to the methyl-substituted amines, the good agreement between the GC model and experimental values for the other methylanilines in Table 9 suggests a different origin, but we currently have no explanation for the failure of the GC model for this particular molecule. As we may learn through other GC models, when we compare to a few other Group Contribution approaches as implemented in the ICAS23 software suite, the deviation with the experimental value for N,N-dimethylaniline is more than 20 kJ/mol for the Marrero-Gani model (so even more than our GC model), but the Constantinou-Gani model is almost spot on with 102.8 kJ/mol (experimental value: 100 kJ/mol). However, for N-methylaniline, the Constantinou-Gani method is 9 kJ/mol off, whereas both our GC model and the Marrero-Gani model values are within chemical accuracy. So, none of these three models accounts with chemical accuracy for all species in Table 9. For the Marrero-Gani method, we found an averaged absolute deviation for all species, N,N-dimethylaniline excepted, of 2.3 kJ/mol, whereas our GC model gives 2.3 kJ/mol, so, in essence, the same averaged performance. Whereas for the Marrero-Gani method three values differ beyond chemical accuracy, for our model, this is only the case for N,N-dimethylaniline, and this despite the fact that the Marrero-Gani method employs more specific benzene substitution parameters such as 1,2,3 or the 1,3,5 pattern, whereas we only differentiate between single, double, or triple substitution [1]. As we have seen that the G4 method generally gives very good values (within chemical accuracy when compared to experiments) for the heat of formation, it is reasonable that we can rely on G4-calculated heats of formation for other anilines too. Interestingly, our GC model value for N,N-diethylaniline of 44.0 kJ/mol agrees very well with the G4 value of 43.1 kJ/mol (Table 9b), as is the case for 2-ethylaniline. The GC model value for 3,5-dimethylaniline is still within chemical accuracy, but 2,6-dimethylaniline is clearly more off (7.4 kJ/mol) but not dramatically so. When we compare to another GC approach, in this case specifically the Marrero-Gani approach, we observe a phenomenon that we have observed before in our series of studies. Whereas one would not expect a deviation for N,N-diethylaniline, as there is no steric hindrance or similar that the GC method does not \begin{table}
\begin{tabular}{c c c c c} \hline
**t-Butyl Benzenes** & **Exp. [42]** & **Exp. [43]** & **Model** & **Model – Exp.** & **ABS (Model – Exp.)** \\ \hline t-butylbenzene & \(-\)22.7 & & \(-\)24.1 & \(-\)1.4 & 1.4 \\ \hline
4-tert-butylfluuene & \(-\)57 & \(-\)53.9 & 3.1 & 3.1 \\ \hline
3-tert-butylfluuene & \(-\)54 & \(-\)53.9 & 0.06 & 0.06 \\ \hline
2-tert-butylfluuene & \(-\)33 & \(-\)53.9 & \(-\)20.9 & 20.9 \\ \hline \end{tabular}
\end{table} 
Table 8: Experimental [42; 43] and current GC model values for the heat of formation for a number of t-butylbenzenes. All values in kJ/mol.