## 2 Results and Discussion
Furthermore, the large difference in relative energies between the lowest energy complex and the next lowest suggests that there is little secondary substitution in the majority of cases; again this is in full agreement with the experimental observations. For example, [PERSON] and coworkers state that aminodefluorination of tetrafluorophthalic acid in anhydrous ammonia gives the 4-amino substituted isomer selectively and in high yield [10], while [PERSON] and coworkers found that amination of 1-nitro-2,4-difluorobenzene gave 98% of the 2-substituted isomer and 2% of the 4-substituted [11]. The relative energy differences between the two different Meisenheimer complexes in these two examples are 12.3 and 2.9 kcal/mol, respectively (see Table 2). Note that this is a clear case of ortho (not para) substitution to the nitro group which is correctly predicted by the Meisenheimer model. Relative energies (in kcal/mol) of the various Meisenheimer complexes for the amination reactions shown in Figure 1. \begin{table}
\begin{tabular}{|c|c|c|c|c|} \hline
**System** & **E (relative)** & **Subst. site** & **System** & **E (relative)** & **Subst. site** \\ \hline \multicolumn{4}{|c|}{**2-acetylamidoheptafluoronaphthalene**} & \multicolumn{2}{c|}{**perfluorotoluene**} & \\ \hline
1-NH\({}_{2}\) & 5.7 & & 2-NH\({}_{2}\) & 6.9 & \\ \hline
3-NH\({}_{2}\) & 5.2 & & 3-NH\({}_{2}\) & 17.5 & \\ \hline
4-NH\({}_{2}\) & 9.7 & & 4-NH\({}_{2}\) & 0.0 & p \\ \hline
5-NH\({}_{2}\) & 7.8 & & & \\ \hline
6-NH\({}_{2}\) & 0.0 & p & **4-aminoperfluorotoluene** & \\ \hline
7-NH\({}_{2}\) & 1.5 & s & 2-NH\({}_{2}\) & 0.0 & p \\ \hline
8-NH\({}_{2}\) & 3.4 & & 3-NH\({}_{2}\) & 12.5 & \\ \hline \multicolumn{4}{|c|}{**perfluoropyridine**} & \multicolumn{2}{c|}{**1-(CF3)-2,3,5,6-tetrafluorobenzene**} \\ \hline
2-NH\({}_{2}\) & 9.9 & & 2-NH\({}_{2}\) & 0.0 & p \\ \hline
3-NH\({}_{2}\) & 23.6 & & 3-NH\({}_{2}\) & 9.1 & \\ \hline
4-NH\({}_{2}\) & 0.0 & p & & \\ \hline \multicolumn{4}{|c|}{**1-(CF3)-2-amino-3,5,6-tetrafluorobenzene**} & \multicolumn{2}{c|}{3-NH\({}_{2}\)} & 10.5 & \\ \hline
2-NH\({}_{2}\) & 0.0 & p & 5-NH\({}_{2}\) & 6.0 & \\ \hline
3-NH\({}_{2}\) & 14.5 & & 6-NH\({}_{2}\) & 0.0 & p \\ \hline \multicolumn{4}{|c|}{**2,3,5,6-tetrafluoropyridine**} & \multicolumn{2}{c|}{**1,3-di(CF3)-2,4,5,6-tetrafluorobenzene**} \\ \hline
2-NH\({}_{2}\) & 0.0 & p & 2-NH\({}_{2}\) & 9.1 & \\ \hline
3-NH\({}_{2}\) & 0.8 & & 4-NH\({}_{2}\) & 0.0 & p \\ \hline \multicolumn{4}{|c|}{**5-NH\({}_{2}\)**} & 26.0 & \\ \hline \multicolumn{4}{|c|}{**2-amino-3,5,6-trifluoropyridine**} & \multicolumn{2}{c|}{**1,3-di(CF3)-4-amino-2,5,6-trifluorobenzene**} \\ \hline
5-NH\({}_{2}\) & 7.9 & & 2-NH\({}_{2}\) & 8.9 & \\ \hline
6-NH\({}_{2}\) & 0.0 & p & 5-NH\({}_{2}\) & 30.5 & \\ \hline \end{tabular}
\end{table} 
Table 2: Relative energies (kcal/mol) of the various Meisenheimer complexes for the amination reactions shown in Figure 1.  
One reaction for which we do predict significant secondary substitution (_i.e._, more than a few percent) is for the amination of 2-acetylamidoheptafluoronaphthalene (Table 2). This was one of the reactions studied in reference [9] along with 2-aminoheptafluoronaphthalene (see Table 1). Experimentally amination of 2-acetylamidoheptafluoronaphthalene gives mainly the 6- and 7-substituted isomers in a 5:1 ratio (similar to the amination of 2-aminoheptafluoronaphthalene except that the ratio is reversed). Our calculations, in which the 6- and 7-substituted Meisenheimer complexes have the lowest energy, with the 7-substituted complex 1.5 kcal/mol higher in energy than the 6-substituted, fully concur with the experimental observations. Note that no experimental data was reported for the amination of 1-trifluoromethyl-2-amino-3,5,6-trifluorobenzene and the depiction in Figure 1--substitution at position 6--is theoretical only, derived from the calculational results shown in Table 2. This is thus a prediction based on our model which is open to experimental confirmation.