Electronic Interactions in Saturated and Unsaturated [1.1.1]‐, [2.1.1]‐, [2.2.1]‐, and [2.2.2]Triblattanes — PE‐Spectroscopic Investigations

Abstract

The He(1)-PE spectra of the parent [1.1.1]-, [2.1.1]-, [2.2.1]-, and [2.2.2]triblattanes 1-4, of their unsaturated or ketonic congeners 5-13 and benzo derivatives 14-20 have been recorded. For 1-4, the energy difference between the highest occupied orbitals (e" and a' mainly localized at the central bicyclo-12.2.2loctane unit) and the subsequent MOs increases with increasing number of ethano bridges. This observation is rationalized by using a first-order perturbation-theoretical approach.Orbitals of nonconjugated x-systems can interact with each other by a "through-space'' (OITS) and/or "through-bond'' mode (OITB)"]. The OITS mode is sometimes subdivided into the terms "homoconjugation"L21 and "spiroc~njugation"[~~. A prerequisite common to all of these OITS types is the spatially confined proximity and orientation of the nonconjugated x-fragment~[~I which can be achieved by their imbedding into a suitable o-system. In fact, record OITS values (2.2 eV) approaching that of classical R,T[ conjugation have been recorded for D2,,-bissecododecahedradiene~'~], in which the specific carbon skeleton enforces unu- 63