A Quantum Chemical and Electrostatic Study of Alkyl and Substituted Benzenonium Cations and Related Molecules: The Effect of Atomic Charge Distribution on Carbocation Energy and Geometry

摘要: Geometries, NMR chemical shifts, atomic charges, and bond orders were calculated at the MP2/6-31G* level of theory for isopropyl, sec-butyl, tert-butyl, benzenonium, six methyl- trifluoromethyl-substituted benzenonium ions. The NPA charges correlate better than CHELPG, MK, AIM with experimental carbon shifts. electrostatic energies isomeric ions, by treatment as point are comparable to their MP2 energy differences. calculations, although classical approximations, provide a qualitative understanding coulombic basis methyl trifluoromethyl substituent effects. It is apparent that these species stabilized having adjacent, oppositely charged atoms (for example, negatively group bonded positive carbon). proposed be termed nucleophilic (rather electron-donating) an electrophilic substituent. In ions in toluene, fluoromethylbenzene, difluoromethylbenzene, benzotrifluoride, endocyclic angle increases increasing electrophilicity An calculation again provides some insight into changes.