COMPARATIVE-STUDY OF ETHANE AND PROPANE CATION RADICALS BY B3LYP DENSITY-FUNCTIONAL AND HIGH-LEVEL AB-INITIO METHODS

A comparative computational study of the cation radicals of ethane and propane is made by using B3LYP density functional and high-level ab i nitio methods [up to QCISD(T)/6-311++G(2df,p) and CBS-APNO model chemi stry]. The properties investigated include the structures and energeti cs of the cation radical isomers, their isotropic hyperfine coupling c onstants, and their carbon-carbon bond dissociation energies, as well as the vertical and adiabatic ionization potentials of the parent mole cules. The computational results are compared with experimental data w here possible. In general, the B3LYP method exhibits good agreement wi th experiment. All of the methods show that the potential energy surfa ces of the two cation radicals are very flat. The electronic origin of this phenomenon and the relationship between the cation radical isome rs of a given species (so-called electromers) are discussed in terms o f a valence-bond model.