Acetylene, isotopic composition

The interaction of an alkyne or alkadiene with deuterium leads to the formation of deuteroalkenes whose isotopic composition yields valuable information regarding possible reaction mechanisms. In an attempt to interpret in detail the deuteroalkene distributions, two approaches have been used. The first, due to Bond [163], is a simplified version of the general theory proposed by Kemball for the hydrogenation of ethylene (see Sect. 3.4) and has been used to interpret the results of the reaction of acetylene with deuterium [163—165]. The method comprises a steady state analysis of the reaction scheme... 

Finally, one more interesting reaction, the mercury-photosensitized polymerization of acetylene should lie mentioned. iShenvood and Gunning (1) showed that a stable mercury compound, probably a mercury carbide, forms in this reaction and that an optimum isotopic composition of 82% 2ll2Hg was obtained in the solid reaction product. These results suggest that, in addition to the primary step leading to the formation of an excited acetylene molecule which was proposed earlier (39), the following two additional primarv routes must also be considered (40) ... 

Using MAS C NMR, the resonances at 127 and 136 ppm were attributed to the cis and trans double bonds and that at 178 ppm was for the carbonyl groups. The composition of the copolymers was determined by elemental analysis, radioassay of C content in the labeled copolymers and NMR. The copolymers were found to have a composition of 95, 90, and 87 mol% acetylene. The molecular weight of the insoluble copolymers was determined by radioassay of the T content after adjustment for the kinetic isotope effect (KEF). At a reaction temperature of —78 C, copolymers in the form of thin film were obtained with A/n = approximately 4000, whereas at a reaction temperature of 25 C, only powder-like products with A/n = approximately 1000 were obtained. The homopolyacetylene was found to have A/ = 11 000 using... 

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