Polyacetylene doping reactions

Oxygen is also a dopant for polyacetylene, but on exposure the conductivity rises to a maximum then rapidly declines as oxidation of the polymer backbone occurs, as shown in Fig. 21. We have no data on the diffusion coefficient as the process is rapid and is masked by the reaction of oxygen with the polymer. The kinetics are first-order, implying that the doping reaction is rapid, goes to less than 1 mol%, and is then followed by irreversible oxidation of the polymer. Based on the observa-... 

Doping by FeCls is usually carried out in nitromethane solution. The anion species is identified by Fe Mossbauer spectroscopy and the extended X-ray absorption fine structure (EXAFS) di7 FeCU. The doping reaction involves dissociation of FeCb in nitromethane (16a) followed by oxidation of polyacetylene by FqC 2 (16b). Thus, the overall doping reaction can be written as equation (16c). 

Electron-donating dopants may reduce polyacetylene or other conjugated polymers giving rise to -type conductivity. Doping occurs when the polymer is immersed in a tetrahydrofuran solution of radical anion/alkalide where the alkalide components can be Li, Na, K, Cs, or Rb, and the radical anion can be naphthalene, anthracene, or benzo-phenone. A doping reaction such as the following occurs (Nph = naphthalene) ... 

The oxidation and/or reduction reactions yield polymeric systems having an extended Jt-electron system along the chain. Doping to the conducting state, in the instance of polyacetylene by exposnre to iodine vapor (p-doping, oxidizing). 

Although it was initially believed that polyacetylene was unstable in contact with water under all conditions, it has been successfully chemically doped in aqueous solutions with no apparent degradation of the material [82] and its electrochemistry has also been investigated [135-137] from which it is clear that no degradation occurs in concentrated aqueous electrolytes. Reaction with water can occur under some circumstances however giving rise to sp3 carbons and carbonyl-type structures [129, 138-141],... 

In TGA studies on the decomposition of iodine-doped polyacetylene, at high heating rates (30°C/min), decomposition becomes explosive at the m.p. of iodine, 113°C. This was attributed to exothermic reaction of liquid iodine with polyacety-lene. 

When the 7r-systerns of two or more double bonds overlap, as in conjugated dienes and polyenes, the 7r-clccIrons will be delocalized. This has chemical consequences, which implies that the range of possible chemical reactions is vastly extended over that of the alkenes. Examples are various pericyclic reactions or charge transport in doped polyacetylenes. A detailed understanding of the electronic structure of polyenes is therefore of utmost importance for development within this field. We will first discuss the structure of dienes and polyenes based on theoretical studies. Thereafter the results from experimental studies are presented and discussed. 

FIGURE 6.2 A film of polyacetylene forms on the inner surface of the reaction vessel, after ethyne gas passes over the catalyst solution of the walls. The paper-thin flexible sheet of polyacetylene is then stripped from the walls before doping. (Photograph by James Kilkelly. Originally published in Scientific American)... 

When poly acetylene is doped with chloric (VII) acid, HCIO4, part of the acid is used to oxidise the polyacetylene and part to provide a counteranion. The oxidation reaction for the acid is given in Equation (6.6). Write a balanced equation for the overall reaction. 

All three compounds (WF6 and MoF6 are best) will bring about a reaction (not a fluorination) that may have synthetic utility at 0CC in l,l,2-trichloro-l,2,2-trifluoroethane (Freon 113) or chloroform they will cleave N,TV-dimethyl- and N-tosylhydrazones and oximes back to the parent carbonyl compounds12,14 (UF6 converts any first-formed aldehydes into acid fluorides1213). All three hexafluorides will convert1215 tertiary amines into carbonyl compounds and carboxylic acids into acid fluorides.16 They also dope polyacetylene to the metallic regime.17... 

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