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The Electronic Structures and Spectra of Pentalene and Heptalene

1964; Oxford University Press; Volume: 37; Issue: 2 Linguagem: Inglês

10.1246/bcsj.37.272

1348-0634

Takeshi Nakajima, Yoshiko Yaguchi, Ryoji Kaeriyama, Yuzo Nemoto,

Spectroscopy and Quantum Chemical Studies

Abstract The semiempirical SCF technique has been applied to pentalene and heptalene. Self-consistency has been achieved for the two symmetry types, D2h and C2h, and the total binding energy examination indicates that in both the molecules the asymmetrical structure (C2h) is more favorable energetically than the symmetrical one (D2h). The calculated uneven charge distributions, the high free valence values, and the low ionization potentials supply the reasons for the instability of these molecules. The theoretical spectral calculations for the asymmetrical structures are in good agreement with the available experimental data. It may be concluded that, in these molecules, there exists a remarkable bond length alternation, and that in this sense they cannot be considered aromatic. They show, rather, characteristics of cyclic polyolefins.