| Abstract
| - The edge-to-face interactions for either axially or facially substituted benzenes are investigatedby using ab initio calculations. The predicted maximum energy difference between substituted andunsubstituted systems is ∼0.7 kcal/mol (∼1.2 kcal/mol if substituents are on both axially and faciallysubstituted positions). In the case of axially substituted aromatic systems, the electron density at the paraposition is an important stabilizing factor, and thus the stabilization/destabilization by substitution is highlycorrelated to the electrostatic energy. This results in its subsequent correlation with the polarization andcharge transfer. Thus, the stabilization/destabilization by substitution is represented by the sum ofelectrostatic energy and induction energy. On the other hand, the facially substituted aromatic systemdepends on not only the electron-donating ability responsible for the electrostatic energy but also thedispersion interaction and exchange repulsion. Although the dispersion energy is the most dominatinginteraction in both axial and facial substitutions, it is almost canceled by the exchange repulsion in theaxial substitution, whereas in the facial substitution, together with the exchange repulsion it augments theelectrostatic energy. The systems with electron-accepting substituents (NO2, CN, Br, Cl, F) favor the axialsubstituent conformation, while those with electron-donating substituents (NH2, CH3, OH) favor the facialsubstituent conformation. The interactions for the T-shape complex systems of an aromatic ring with othercounterpart such as H2, H2O, HCl, and HF are also studied.
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