LINEAR AND ANGULAR INTERACTIONS IN DISTELLENES - PHOTOELECTRON-SPECTRA AND AB-INITIO SCFMO STUDIES

The photoelectron spectra of ylidene-2,2'-bis(tricyclo[3.3.0.0(3,7)]oc tylidene) (12), syn- and -2,2'-bis(tricyclo[3.3.0.0(3,7)]octane)-4,4'- dione (13 and 14), syn- and -2,2'-bis(tricyclo[3.3.0.0(3,7)]octylidene )-4'-one (15 and 16), and lidene-2,2'-bis-(tricyclo[3.3.0.0(3,7)]octyl idene) (18) have been recorded. The energy difference between the 2p-t ype lone pairs of the angular oriented oxygen atoms of 13 and 14 amoun ts to 0.6 eV, while the corresponding energy difference in 4, where th e oxygen atoms are linearly orientated, is 0.2 eV. For 3 and 12,in whi ch the terminal pi-bonds are arranged linearly, the difference between the first two peaks in their spectra is 0.4-0.5 eV, while the angular arrangement of the terminal pi-bonds in 18 gives a splitting of only 0.2 eV. Hartree-Fock SCF calculations, using a 6-31G basis set, have been used to interpret the photoelectron spectra of 12-16, 18, and 19. The interactions between the sigma frame and the n and pi orbitals in these molecules have been investigated and analyzed in terms of the t hrough-space through-bond concept. It is concluded that a maximum inte raction between pi bonds is attained, if they are arranged in a linear fashion, while the interaction between pi bonds and keto groups reach es its maximum in an angular orientation.