| Abstract
| - The structure and the stability of various cyclopentadienides, which involve 6π, 10π, 14π, and 22πelectrons, are investigated from computations at various levels of theory as well as from orbitalinteraction analyses. The reason that some of the cyclopentadienides are stabilized and others aredestabilized by the introduction of aromatic rings is discussed in terms of absolute hardness andorbital interaction. Cyclopentadienide, a special 6π-electron system, has the largest value of absolutehardness among the condensed cyclopentadienides investigated; thus this carbanion resists bothoxidation and reduction most strongly. The absolute hardness decreases when aromatic rings areintroduced to cyclopentadienide to form condensed cyclopentadienides, depending on the way theyare connected. Computed values of the ionization potential and oxidation potentials measured insolution have a linear correlation within isomers of the same size, but are not in agreement fordifferent sets of isomers. Solvent effects on the ionization potential are assessed by performingself-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 6π- and10π-electron systems, compared to larger ones and that addition of condensed aromatic ringsintrinsically stabilizes the formed condensed cyclopentadienides with respect to ionization potential.
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