title: Orbital Interactions and Solvent Effects Determining the Stability of Condensed Cyclopentadienides in Solution.
abstract: The structure and the stability of various cyclopentadienides, which involve 6pi, 10pi, 14pi, and 22pi electrons, are investigated from computations at various levels of theory as well as from orbital interaction analyses. The reason that some of the cyclopentadienides are stabilized and others are destabilized by the introduction of aromatic rings is discussed in terms of absolute hardness and orbital interaction. Cyclopentadienide, a special 6pi-electron system, has the largest value of absolute hardness among the condensed cyclopentadienides investigated; thus this carbanion resists both oxidation and reduction most strongly. The absolute hardness decreases when aromatic rings are introduced to cyclopentadienide to form condensed cyclopentadienides, depending on the way they are connected. Computed values of the ionization potential and oxidation potentials measured in solution have a linear correlation within isomers of the same size, but are not in agreement for different sets of isomers. Solvent effects on the ionization potential are assessed by performing self-consistent reaction field calculations, the results being in excellent agreement with experiments. It is demonstrated that the solvent effects are significant in small cyclopentadienides of 6pi- and 10pi-electron systems, compared to larger ones and that addition of condensed aromatic rings intrinsically stabilizes the formed condensed cyclopentadienides with respect to ionization potential.
authors.affiliation: Department of Molecular Engineering, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan, Institute for Fundamental Chemistry, 34-4 Takano-Nishihiraki-cho, Sakyo-ku, Kyoto 606-8103, Japan, and Department of Energy and Hydrocarbon Chemistry, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Kazunari
authors.initials: K
authors.lastname: Yoshizawa
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Yahara
authors.forename: Aya
authors.initials: A
authors.lastname: Taniguchi
authors.forename: Tokio
authors.initials: T
authors.lastname: Yamabe
authors.forename: Tomomi
authors.initials: T
authors.lastname: Kinoshita
authors.forename: Ken'ichi
authors.initials: K
authors.lastname: Takeuchi