The ionization energies of bent and twisted double bonds. Part II. Tricyclo[4.2.2.2 2,5] Dodecadiene-1 (2),5 (6)

• Published in: Journal of electron spectroscopy and related phenomena 1983, Vol.31 (3), p.369-381
• Main Authors: Honegger, Evi, Heilbronner, Edgar, Wiberg, Kenneth B.
• Format: Article
• Language: English
• ISSN: 0368-2048; 1873-2526
• DOI: 10.1016/0368-2048(83)85083-X

The electronic structure of the title compound (1) has been investigated using He(Iα) PE spectroscopy and assuming the validity of Koopmans' theorem. It is found that: (a) in analogy to the situation prevailing in the cyclophanes, hyperconjugation of the out-of-phase linear combination of the π-orbitals with the ethano-bridge σ orbitals is symmetry-forbidden; (b) in agreement with the ideas developed in Part I of this series [1], the strong local B 1u-type bending of the ethylene moieties does not affect their basis energy significantly; and (c) the “through-space” coupling of the two double-bond π orbitals is of the same order as the benzene π-orbital coupling in [2 n ] cyclophanes, even if the net contribution to the repulsion of the two double bonds is probably small. Because of the near degeneracy of the HOMO and HOMO — 1 of 1, the ground state of the radical cation 1 + cannot be determined uniquely: it is either 2 A g or 2 B 1u.