Polyacetylenic structures

Furthermore, the fact that the scan exhibits two peaks suggests the presence in the basic polyacetylene structure of at least two (if not more) different structural sites for the doping process, as effectively confirmed by independent structural studies (Shacklette et al, 1985). Finally, the... 

Homocoupling of terminal acetylenes first described by Glaser in 1869 [1] occurs in presence of a base, a copper(I) salt (usually CuCl) and dioxygen (Scheme la). Because of the widespread occurrence of di- and polyacetylenic structures in... 

Figure 1 Regular (Model I) and alternating (Model II) trans-polyacetylene structures. The unit cells are surrounded by broken lines...

For the corresponding polyacetylene structures see Figures 1 and 2. 6 Position of the Fermi level. e Half filled band. 

Using such a procedure, a sample of the microporous polypropyl-ene/polyacetylene structure consisting of 5.7% polyacetylene was doped to the maximum level. 

Property Microporous Polypropylene Alone Microporous Polypropylene/ Polyacetylene Structure... 

Micron Rated Microporous Polypropylene/Polyacetylene Structures. 

Procedure 12 Attempt to Prepare a Nylon 6/Polyacetylene Structure. 

Two recent ab-initio studies are devoted to the determination of the ground-state structure of Cg. Parasuk and AlmlOf concluded that the cyclic polyacetylenic structure ( Ag) and the linear cumulenic g state are essentially isoenergetic [260]. However, the choice of basis sets and methods (MRCI modified coupled-pair functional, MCPF) heavily affects the difference in energy between the linear and cyclic forms of Cg, and so the results are quite uncertain. On the other hand, Slanina et al. proposed a nonplanar Z)2d symmetrical cyclic structure as the minimum-energy structure of Cg [261]. According to their MP2/6-31G calculations, this form is 13 kcal/mol lower in energy than the planar Qa structure. Unexpectedly, all the C-C bond lengths in the species are equivalent (1.339 A). DFT calculations favor the linear structure as compared with a planar cyclic one, but nonplanar species seem to have not been considered in this study [236]. 

Density functional theory was also applied to this problem. The cumulenic Dg, form IS turned out to be a minimum structure at the B-LYP level of DFT using a 6-31G basis set, while the fully symmetrical structure 13 is 2.4 kcal/mol higher in energy. Unfortunately, it was not possible to localize a polyacetylenic structure with the DFT methods used. The same trend holds for Cjo and Cj4, other candicates for Htickel aromaticity the and D-j symmetrical cumulenic structures are minima on the potential energy surface polyacetylenic isomers are not stationary points using DFT methods. 

Of the various halogen derivatives of the polyacetylenes structures 16-19 have been investigated by PE spectroscopy. As already stated in the previous section, there is a correlation found between the observed orbital energies of the symmetric dihalodiacetylenes 17 and the valence state ionization energies of the free halogen atoms. ... 

Figure 1.15. (a) Comparison between data (circles) and calculated diffraction profile (solid line) for commensurate Na-doped polyacetylene structure (inset) (b) comparison between data (circles) and calculated difftaction profile (solid line) for discommensurale-domain structure shown in inset. Inset left Plot of linear-domain wall density (in inverse polyacetylene lattice constant units) versus cell open-circuit voltage. (Reproduced Irom ref 97 with kind permission. Copyright (1987) American Physical Society.)... 

Saunders, R. S., Cohen, R. E., and Schrock. R. R., Synthesis and characterization of diblock copolymer films containing self-assembled polyacetylene structures. Macromolecules, 24, 5599-.5605 (1991). 

Mycomycin, which was isolated by Celmer and Solomons from the culture fluid of the actinomycete, Nocardia acidophilus, was shown to contain a polyacetylenic structure and also an optically active allene unit (XLII). Van t Hoff had predicted that the aUene unit should show optical activity, but mycomycin provided the first example of its existence in nature. Nemotin (XLIII) and nemotinic acid (XLIV), which are formed by Poria corticola and Poria tenuis, are also allenes. A related compound, odyssic acid (XLV), is produced by the same fungi. 

FIGURE 1.21. Various polyacetylene structures, both degenerate and nondegenerate structures shown. 

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