Orbital interactions. XI. Application of photoelectron spectroscopy to the study of orbital interactions in some 2- and 9-substituted octahydrodimethanonaphthalenes

The photoelectron spectra of some 2- and 9-substituted (1x,4x,4aβ,5β,8β,8aβ)-1,2,3,4,4a,5,8,8a-octahydro-1,4:5,8-dimethanonaphthalenes, (1)-(6), and (12), and their perhydro analogues, (1')-(6'), and (12'), were obtained in order to assess the magnitude and nature of orbital interactions in these molecules. The πcc Ip of the ketone (12) was found to be 0.1 eV higher than that of the hydrocarbon (1) and is thought to be due to the presence of orbital interactions through bonds in the former molecule. Through-space and through-bond interactions in the ketone (6) are responsible for increasing the πcc Ip by 0.33 eV with respect to that of (1) whereas through-space interactions are solely responsible for the lowering of the πcc Ip of the syn-ether (5) 0.36 eV with respect to the anti isomer (3). Strong intramolecular OH…π bonding in the alcohol (4) results is an increase in πcc by 0.33 eV and a decrease in the no Ip by 0.42 eV both with respect to the corresponding ionizations in the anti-alcohol (2).