SYNTHESIS AND PROPERTIES OF MEDIUM-SIZED (C9-C12) CARBOCYCLIC DIACETYLENES

The syntheses of 1,5-cyclononadiyne (3), 1,5-cyclodecadiyne (4), 1,5-cycloundecadiyne (5), 1,6-cycloundecadiyne (6), 1,6-cyclododecadiyne (7), and 1,7-cyclododecadiyne (8) have been carried out. Diacetylenes 3 and 4 are prepared from 5-cyclononynone and 5-cyclodecynone, respectively. Compounds 5-8 are synthesized from cyclic diones by thermolysis of the corresponding bisselenadiazoles. The obtained cyclic diacetylenes are further characterized by their bis(hexacarbonyldicobalt) complexes. The geometrical parameters of 3-8 were calculated with force field and semiempirical methods. From the structural data, a correlation between the C-13 resonance of the sp-hybridized carbon atoms adjacent to the ethano bridge in 3-5 and the corresponding resonance of the symmetric dialkynes 1,5-cyclooctadiyne (1), 1,6-cyclodecadiyne (2), and 1,7-cyclododecadiyne (8) with the bending angle at this center can be verified. The PE spectra of 3-8 have been recorded, and an interpretation of the bands in the low-energy region is presented. It is found that the splitting of the PE bands that are assigned to the in-plane pi-MO's (pi-i) strongly depends on the size of the methylene bridge. In the case of a propano bridge (e.g., in 3, 6, and 7), the splitting between pi-i- and pi=i+ is relatively large. The splitting of the bands that are assigned to the out-of-plane pi-MO's (pi-o) decreases with increasing transannular distance.