Dehydrogenated fragments

This is a general feature equally for the methyl derivatives, as, for example, Figure 3(6) for toluene and Figure 4(a) for p-xylene show. It will be noticed, that the efficiency curve for the dehydrogenated fragmentations closely resembles that of the parent ions, being much depressed. 

However, like other benzene derivatives, the main dissociation process is the detachment of an H atom from the parent molecular ion. Moreover, as shown in Figure 7(6) a small amount of the molecular ion with two H atoms lost is formed from benzylamine. A similar twofold photodehydrogenation process has been previously observed by us for hydrazine.17 Figure 6 shows that the spectral threshold for the appearance of these doubly dehydrogenated fragments is the same as that of the singly dehydrogenated ones. 

The cylization of alkylaromatics over platinum catalysts is usually accompanied by isomerization, hydrogenation and dehydrogenation, fragmentation (i.e., hydrogenolysis and cracking), and other reactions. 

Ethylene A general feature of unsaturated hydrocarbon adsorption on clean transition-metal surfaces is that it is largely irreversible. In other words, when one adsorbs an unsaturated hydrocarbon onto a transition-metal surface at low temperature and then heats the surface, the adsorbed molecule, rather than desorbing molecularly, will decompose to evolve hydrogen and leave the surface covered with the partially dehydrogenated fragments or carbon. 

On the catalysts with large metal crystallites size, the strong adsorption of the dehydrogenated species leads to the formation of coke deposits. Other mechanism involves the formation of highly dehydrogenated fragments that may combine to form more toxic coke deposits. 

The significance of the above-described work is that in all of the presently developing coal liquefaction processes, the initial step in the conversion is thermal fragmentation of the coal structure to produce very fragile molecules which are highly functional, low in solubility, and extremely reactive toward dehydrogenation and char formation. A more detailed discussion of the chemical nature of these initial products has been presented elsewhere (4). ... 

Related dehydrogenation processes are known as in the aromatization of the A ring of steroids, which was achieved by using the Cp Ru+ fragment. Such a process occurs via a series of C-O, C-H and C-C bond activations (Equation (24)).34... 

The concept of site isolation is important in catalysis. On metal particles one usually assumes that ensembles of metal atoms are necessary to activate bonds and to accommodate the fragments of molecules that tend to dissociate or to recombine. We present here three examples of such effects the dehydrogenation of decane into 1-decene, the dehydrogenation of isobutane into isobutene and the hydrogenolysis of acids or esters into aldehydes and alcohols. In most cases the effect of tin, present as a surface alloy, wiU be to dilute the active sites, reducing thereby the yield of competitive reactions. 

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