Labeled atoms reactions three-atom complex

Reactions of molecules with labeled carbon (13C, UC). Gault and his co-workers pioneered (see, for review, 157) the use of 13C-labeled molecules in experiments by which the operation of adsorbed complexes with either three or five C atoms involved could be tested (see below). 14C has been repeatedly used in problems concerning the dehydrocyclization and aromatization reactions (157,163-166). The authors (163-166) in their research combined the use of labeled molecules with the third method, the study of archetype molecules. 

An ingenious method for detecting the transfer of the terminal phosphate of ATP in ATP-coupled enzyme reactions has been devised, If an enzyme becomes reversibly phosphorylated, and the /9-phosphate of the bound ADP is free to rotate, an isotopic label in the terminal oxygen bridge will become scrambled between three oxygen atoms (Scheme 2). In order to demonstrate the formation of a complex... 

The concentration of zinc accelerator-thiolate complexes in the rubber is not the only factor determining the balance of the two reactions in NR. Both the rate of desulfuration of polysulfide crosslinks and the rate of their thermal decomposition depend upon the positions of attachment of the sulfur chains to the backbone rubber chains and the detailed structure of the hydrocarbon at the ends of the crosslinks. In the course of normal accelerated vulcanization there are three different positions of attack on the polyisoprene backbone two of these are methylene groups in the main chain (labelled d and a in 3), and the third is the side chain methyl group (labelled b in 3). Direct analysis of the distribution of the sites of attack cannot yet be made on actual rubber vulcanizates, and information has had to be obtained solely by sulfuration of the model alkene 2-methyl-2-pentene and, more recently, 2,6-dimethyl-2,6-octadiene. The former (4) models the a-methylic site but only one of the two a-methylenic sites of polyisoprene the latter (5) models all three sites, but at the present time these are not all supported by the synthesis of relevant sulfides. Because allylic rearrangements are common in subsequent reactions of the sulfurated rubber, sulfur substituents appear not only on allylic carbon atoms but on isoallylic carbon atoms. Thus, from 2-methyl-2-pentene, the groups shown in Scheme 2 are formed. 

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