Deuterium exchange reactions, compensation

The exchange reactions of methane with deuterium over several metals (21, 39,146,147,195, 215, 216, 229) exhibited compensation behavior (Table III, G), as has been pointed out previously (3). No such relationship was found in the data available for exchange reactions of C2-C6 hydrocarbons. This is consistent with discussion given above (see Section III, B, 4) in which it was concluded that the differences in the kinetic behavior of the exchange reactions between methane and the other hydrocarbons varied with the individual metals concerned. 

By contrast with the radiation-induced procedures, isotope exchange reactions catalyzed by Group VIII transition metals are applicable to both deuterium and tritium labeling of heterocyclic compounds. Because of recent mechanistic developments in this field, it is possible to predict with some degree of certainty the reactivity of a molecule for deuteration and also for moderate levels of tritiation. If compensation for additional radiation-induced interactions is made, then the theory also satisfactorily explains high specific activity tritiations. 

In connection with the interpretation of these trends it should be noted that in some reactions (e.g., ethylene hydrogenation) the activation energy remains substantially constant and the frequency factor changes as the metal is varied, while in other reactions (e.g., deuterium-ammonia exchange) the reverse is the case. In the exchange of deuterium with saturated hydrocarbons, a compensation effect (Cremer, 128) has been noted. The significance of these different patterns is not clear. 

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