title: Substituent effects on the edge-to-face aromatic interactions.
abstract: The edge-to-face interactions for either axially or facially substituted benzenes are investigated by using ab initio calculations. The predicted maximum energy difference between substituted and unsubstituted systems is approximately 0.7 kcal/mol (approximately 1.2 kcal/mol if substituents are on both axially and facially substituted positions). In the case of axially substituted aromatic systems, the electron density at the para position is an important stabilizing factor, and thus the stabilization/destabilization by substitution is highly correlated to the electrostatic energy. This results in its subsequent correlation with the polarization and charge transfer. Thus, the stabilization/destabilization by substitution is represented by the sum of electrostatic energy and induction energy. On the other hand, the facially substituted aromatic system depends on not only the electron-donating ability responsible for the electrostatic energy but also the dispersion interaction and exchange repulsion. Although the dispersion energy is the most dominating interaction in both axial and facial substitutions, it is almost canceled by the exchange repulsion in the axial substitution, whereas in the facial substitution, together with the exchange repulsion it augments the electrostatic energy. The systems with electron-accepting substituents (NO2, CN, Br, Cl, F) favor the axial substituent conformation, while those with electron-donating substituents (NH2, CH3, OH) favor the facial substituent conformation. The interactions for the T-shape complex systems of an aromatic ring with other counterpart such as H2, H2O, HCl, and HF are also studied.
authors.affiliation: National Creative Research Initiative Center for Superfunctional Materials, Department of Chemistry, Division of Molecular and Life Sciences, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, Pohang 790-784, Korea.
authors.forename: Eun Cheol
authors.initials: EC
authors.lastname: Lee
authors.forename: Byung Hee
authors.initials: BH
authors.lastname: Hong
authors.forename: Ju Young
authors.initials: JY
authors.lastname: Lee
authors.forename: Jong Chan
authors.initials: JC
authors.lastname: Kim
authors.forename: Dongwook
authors.initials: D
authors.lastname: Kim
authors.forename: Yukyung
authors.initials: Y
authors.lastname: Kim
authors.forename: P
authors.initials: P
authors.lastname: Tarakeshwar
authors.forename: Kwang S
authors.initials: KS
authors.lastname: Kim
mesh_terms: D001555:Benzene Derivatives / Q000737:chemistry*; D001704:Biopolymers / Q000737:chemistry; D008958:Models, Molecular; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D001555:Benzene Derivatives; D001704:Biopolymers