Hydrogen availability to the catalyst

As a result of rather extensive work on the hydrogenation of olefins 139,151 mechanism originally proposed by Horiuti and Polanyi is currently accepted  

This process accounts for most of the observations relating to product stereochemistry, double bond isomerism, deuterium exchange and other features encountered in the hydrogenation and deuteration of olefins. 140-142,144 addition of hydrogen to the double bond proceeds in 

The hydrogen concentration at the catalyst surface can also be modified 

While the foregoing concepts have been utilized to rationalize the product distribution obtained on hydrogenation of a number of monocyclic olefins, it should be noted that the effect of pressure on the stereochemistry of hydrogenation of steroidal double bonds has not been critically evaluated. 

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II. Factors which Influence Product Stereochemistry / 111 Hydrogen availability to the catalyst /111... 

As was observed in neutral solvents, increasing the hydrogen availability to the catalyst resulted in a decrease in the amount of cis product formed, as shown in Fig. 6. Under high hydrogen availability conditions, equilibration of the adsorbed carbonium ion does not occur and, hence, more of the trans-saturated product is obtained. 

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