An electron momentum spectroscopy study of π orbitals of norbornadiene and 1,4-cyclohexadiene: evidence for through-space and through-bond interactions

Electron momentum spectroscopy is applied to determine the character of the two outermost π orbitals of norbornadiene and 1,4-cyclohexadiene. From comparisons of observed and calculated electron momentum distributions, the highest occupied molecular orbital is experimentally identified as π− in the former and as π+ in the latter.