Hydrogen-deuterium exchange relationship

When applied to hydrogen exchange reactions in benzene derivatives containing a deuterium or tritium atom in the ith position, the relationship becomes simplified and assumes the form... 

The evidence also indicates that the deuteration of benzene differs markedly from the deuteration of aliphatic olefines in that very little redistribution occurs and that the process seems to be limited to the addition of deuterium without additional exchange. Furthermore, the order of activities of different metals for the deuteration of benzene is quite unlike the order for the hydrogenation of ethylene and bears no relationship to the percentage d-bond character of the intermetallic bonds. 

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