Application of photoelectron spectroscopy to intramolecularly hydrogen-bonded systems. Part IV. π-Systems; the photoelectron spectra of syn- and anti-7-norbornenol

Abstract

In an effort to determine the effect of an intramolecular hydrogen bond on the ionization energy of a simple π-system, the photoelectron spectra of syn- and anti-7-norbornenol have been determined. The difference in the ionization energy of the π(C—C) and nÖH orbitals is 0.30 eV for the former, and 0.85 eV for the latter. The photoelectron spectrum of the syn- isomer shows that the π(C—C) bond is roughly 0.2 eV more difficult to ionize than its counter-part in the non-hydrogen bonded geometric isomer and has been interpreted as arising from hydrogen bond induced stabilization of the π-bond. That the spectral differences in the alcohols is not simply due to differing orbital interactions between the two isomers can be demonstrated by the photoelectron spectra of syn- and anti-7-methoxynorbornene. In these systems which allow no possibility of hydrogen bonding the π(C—C) – nÖR difference is the same for both isomers.