## 3 Results
### Substituted Benzenes
#### 3.3.3 Phenols  
Data on alkylsubstituted phenols are shown in Table 10. Regarding the GC parameters, an additional OH-phenyl group interaction parameter was introduced and has a value of +7 kJ/mol. This leads to good agreement between experimental and GC model values, with an averaged absolute deviation of 2.8 kJ/mol. The G4 quantum values, adopted from [PERSON] c.s. [19], reveal an averaged absolute difference of 1.8 kJ/mol. Two GC model values are slightly beyond chemical accuracy, namely, for 4-ethylphenol and 2,4-dimethylphenol. Somewhat surprisingly, the G4 value for 3-methylphenol shows a difference of 6.4 kJ/mol compared to the experimental value ([PERSON] c.s. [34]), whereas the G4 value is in agreement with our GC model within chemical accuracy. Regarding the three methylphenols, the experimental heats of formation, as presented in Table 10. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{6}{c}{(**a**)} \\ \hline
**Anilines** & **Exp.** & **Model** & **Model – Exp.** & **G4** & **G4 Avgd.** & **G4 Avgd. – Exp.** \\ \hline aniline (benzenamine) & 87 & 90.5 & 3.5 & 87.6 & 87.6 & 0.6 \\ \hline
2-methylaniline (o-toluidone) & 52.6 & 54.1 & 1.5 & 51.7 & 51.7 & \(-\)0.9 \\ \hline
3-methylaniline (m-toluidine) & 57 & 54.1 & \(-\)2.9 & 54.1 & 54.1 & \(-\)2.9 \\ \hline
4-methylaniline (p-toluidine) & 57 & 54.1 & \(-\)2.9 & 56.5 & 56.5 & \(-\)0.5 \\ \hline
2,4-dimethylaniline & 23.2 & 24.3 & 1.1 & 21.0 & 21 & \(-\)2.2 \\ \hline
2,5-dimethylaniline & 23.9 & 24.3 & 0.4 & 19.0 & 19 & \(-\)4.9 \\ \hline N-methylaniline & 90.9 & 87.1 & \(-\)3.8 & 93.1 & 93.1 & 2.2 \\ \hline N-ethylaniline & 66.5 & 66.5 & 0.0 & 64.5 & 65.6 & \(-\)0.9 \\ \hline N,N-dimethylaniline & 100 & 85.3 & \(-\)14.7 & 98.9 & 98.9 & \(-\)1.1 \\ \hline Benzylaniline & 205.8 & 199.4 & \(-\)6.4 & & & \\ \hline averaged absolute difference & & & 2.4 & & 2.1 \\ \hline \multicolumn{6}{c}{(**b**)} \\ \hline
**Anilines** & & **Model** & **G4 Avgd.** & **MG ICAS23** \\ \hline
2,6-dimethylaniline & & 24.3 & 16.9 & 25.3 \\ \hline
3,5-dimethylaniline & & 24.3 & 20.7 & 19.9 \\ \hline
2-ethylaniline & & 33.5 & 32.8 & 36.2 \\ \hline N,N-diethylaniline & 44.0 & 45.7 & 37.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: (**a**) Experimental, present GC model, and G4 model values for the heat of formation for a number of anilines. All values in kJ/mol. Experimental data from [PERSON] c.s. (aniline and [PERSON] c.s. (all other species). In the averaged absolute difference for the model-exp value (1.87 kJ/mol) we have excluded the N,N-dimethylaniline value (14.7 kJ/mol). (**b**) Heats of formation as calculated by our current GC model, [PERSON]’s G4 quantum results [16; 17; 18], and the Marrero–Gani GC approach [10] as implemented in the ICAS software suite [41]. Table 10 reveal the most negative value for 3-methylphenol, a variety of quantum method results, including CBS-QB3, G2, G3, G4 (all from Ref. [19]), T1 [45] (actual results obtained with the Spartan program [31]), and B3 LYP relative energy calculations (present work), reveal that there is a monotonic decrease from 2-methylphenol to 4-methylphenol. In other words, according to all these methods, 2-methylphenol has the most negative heat of formation, which puts serious doubt on the experimental value for 3-methylphenol. Therefore, we conclude that our GC model performs very well, with almost all individual values within chemical accuracy and the exceptions not much beyond (less than 5 kJ/mol). The additional OH-phenyl group interaction parameter introduced here has a value of +7 kJ/mol. One may question whether this parameter should be seen at an identical base as the interaction parameter for an alkyl substitution for which we previously established a parameter value of +6 kJ/mol. The potential advantage would be that we have one parameter less, which is generally good for a model with many parameters. With a value of +6 kJ/mol, the results for the phenols are still acceptable throughout.