PE-SPECTROSCOPIC INVESTIGATION OF NONCONJUGATED PI,PI INTERACTIONS IN(SECO)DODECAHEDRADIENES - ON THE ROUTE TO AN EXPERIMENTAL ETHYLENE ETHYLENE CYCLOADDITION REACTION COORDINATE/

Nature and extent of nonconjugated pi,pi interactions in (bis)secodode cahedradienes and (pentagonal, non-pentagonal) dodecahedradienes with transannular pi,pi distances ranging from ca. 2.8 to ca. 3.5 Angstrom - representing well defined points on the D-2h [pi(2) + pi(2)] reactio n coordinate - were studied by PE spectroscopy. The pi,pi splitting of 0.68 eV measured at the largest pi,pi distance of ca. 3.5 Angstrom (1 ,16-dodecahedradiene 3a) was attributed to ca. 50% each of through-spa ce and through-bond conjugation (analysis of precanonical MOs).