THE PI-STAR NEGATIVE-ION STATE OF (E)-CYCLOOCTENE

The vertical electron attachment energy (AE) for the pi* negative ion state of (E)-cyclooctene (1) has been determined by electron transmission spectroscopy to be 1.72 eV. Analysis of the pi* wave function of 1 at optimal levels of basis set for agreement with experiment indicates that any stabilization of pi* owing to distortion of the double bond is largely counteracted by antibonding interactions between pi* of the double bond and orbitals of the alkyl bridge. This accounts for the fact that AE(pi*) of 1 is greater than expected and its difference from AE(pi*) of (Z)-cyclooctene is less than expected on the basis of simpler models.