Small and Medium Rings, 77¹⁾ Nonconjugated π,π Interactions Approaching Classical π,π Conjugation – PE‐Spectroscopical Investigation of the 7,8;12,19‐Diseco‐1,16‐dodecahedradiene System

Abstract

Transannular (orbital) interactions in compounds 1 – 9 are studied by means of He( I α)‐PE spectroscopy. Unusually strong through‐space‐dominated π,π interaction is found to be operative in the nonconjugated 1,6‐dienes 1, 2, 7 , and 8 . The π,π splitting of 1.9 eV for disecododecahedradiene 1 is even surpassed by the record value of 2.2 eV for disecodienedione 2 , which almost equals that in 1,3‐butadiene (2.46 eV). The experimental results are explained by computational methods, especially by analyses of the precanonical MOs.