## 3 Results
### Substituted Benzenes
#### 3.3.7 Benzoic Acids
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Benzo Acids** & **Exp.** & **Model** & **Model – Exp.** & \begin{tabular}{c} **ABS** \\ **(Model – Exp.)** \\ \end{tabular} & \begin{tabular}{c} **G4** \\ **Avgd.** \\ \end{tabular} & \begin{tabular}{c} **ABS** \\ **(G4 – Model)** \\ \end{tabular} & \begin{tabular}{c} **ABS** \\ **(G4 – Exp.)** \\ \end{tabular} & \
\begin{tabular}{c} **ABS** \\ **(G4 – Exp.)** \\ \end{tabular} &
\begin{tabular}{c} **MG in** \\ **ICAS23** \\ \end{tabular} \\ \hline benzoic acid & \(-\)294.1 & \(-\)294.5 & \(-\)0.4 & 0.4 & \(-\)296.9 & 2.4 & 2.8 & \(-\)294.3 \\ \hline
2-methylbenzoic acid & \(-\)320.6 & \(-\)330.9 & \(-\)10.3 & 10.3 & \(-\)323.7 & 7.2 & 3.1 & \(-\)324.0 \\ \hline
3-methylbenzoic acid & \(-\)327.9 & \(-\)330.9 & \(-\)3.0 & 3.0 & \(-\)330.9 & 0.0 & 3.0 & \(-\)325.9 \\ \hline
4-methylbenzoic acid & \(-\)330.4 & \(-\)330.9 & \(-\)0.5 & 0.5 & \(-\)332.0 & 1.1 & 1.6 & \(-\)326.0 \\ \hline
2-ethylbenzoic acid & \(-\)340.6 & \(-\)351.5 & \(-\)10.9 & 10.9 & \(-\)343.5 & 8.0 & 2.9 & \(-\)341.7 \\ \hline
3-ethylbenzoic acid & \(-\)346.7 & \(-\)351.5 & \(-\)4.8 & 4.8 & \(-\)352.0 & 0.5 & 5.3 & \(-\)343.5 \\ \hline
4-ethylbenzoic acid & \(-\)355.6 & \(-\)351.5 & 4.1 & 4.1 & \(-\)352.9 & 1.4 & 2.7 & \(-\)343.7 \\ \hline
3.5-diethylbenzoic acid & \(-\)407.8 & \(-\)402.0 & 5.8 & 5.8 & \(-\)408.0 & 6.1 & 0.2 & \(-\)393.3 \\ \hline
2-methoxybenzoic acid & \(-\)433.8 & \(-\)446.5 & \(-\)12.7 & 12.7 & \(-\)432.7 & 13.8 & 1.1 & \(-\)445.0 \\ \hline
3-methoxybenzoic acid & \(-\)446.1 & \(-\)446.5 & \(-\)0.4 & 0.4 & \(-\)452.3 & 5.8 & 6.2 & \(-\)446.8 \\ \hline
4-methoxybenzoic acid & \(-\)451.9 & \(-\)446.5 & 5.4 & 5.4 & \(-\)456.2 & 9.7 & 4.3 & \(-\)447.0 \\ \hline
2-aminobenzoic acid & \(-\)296.0 & \(-\)288.5 & 7.5 & 7.5 & \(-\)306.9 & 18.4 & 10.9 & \(-\)295.5 \\ \hline
3-aminobenzoic acid & \(-\)283.6 & \(-\)288.5 & \(-\)4.9 & 4.9 & \(-\)293.7 & 5.2 & 10.1 & \(-\)297.4 \\ \hline
4-aminobenzoic acid & \(-\)296.7 & \(-\)288.5 & 8.2 & 8.2 & \(-\)299.9 & 11.4 & 3.2 & \(-\)297.6 \\ \hline
2-tert-butylbenzoic acid & \(-\)376.1 & \(-\)403.1 & \(-\)27.0 & 27.0 & \(-\)375.3 & 27.8 & 0.8 & \(-\)393.9 \\ \hline
3-tert-butylbenzoic acid & \(-\)400.8 & \(-\)403.1 & \(-\)2.3 & 2.3 & \(-\)409.5 & 6.4 & 8.7 & \(-\)395.8 \\ \hline
4-tert-butylbenzoic acid & \(-\)398.5 & \(-\)403.1 & \(-\)4.6 & 4.6 & \(-\)409.6 & 6.5 & 11.1 & \(-\)396.0 \\ \hline \hline \multicolumn{8}{c}{averaged absolute difference} & 6.6 & 7.8 & 4.6 & \\ \hline \multicolumn{8}{c}{averaged absolute difference without 2-’ substituted species} & 3.7 & \\ \hline \hline \end{tabular}
\end{table} 
Table 14: Experimental, present GC model, and conformationally averaged G4 model values for the heat of formation for benzoic acids. All values in kJ/mol. Experimental values from [PERSON] c.s. [34] except for the methylbenzoic acids [48]. values is reasonably good for 3,5-diethylbenzoic acid, which is, as expected, not suffering from steric overlap effects between the substituents. The aminobenzic acids reveal a somewhat different behaviour as the 2- and 4-aminobenzoic acids have an identical heat of formation (within experimental accuracy) and both are more stable than 3-aminobenzoic acid by some 13 kJ/mol. The error in the experimental results was given by [PERSON] c.s. as 3.9 kJ/mol for 3-aminobenzoic acid and 3.8 kJ/mol for 4-aminobenzoic acid (for 2-aminobenzoic acid, the given error is 1.3 kJ/mol). This implies that the GC model values for 3- and 4-aminobenzoic acid are in fact within experimental accuracy from the experimental values. Finally, when we consider the good performance of the G4 method for the cases discussed before, as well as the majority of cases in Table 14, we see that for 2- and 3-aminobenzoic acid as well as 3- and 4-t-butylbenzoic acid, the difference between the conformationally averaged G4 value and the experimental value is around 10 kJ/mol. In three out of four, there are no steric effects and so no potential weak interactions which may not be well accounted for.