Topside addition of hydrogen

A third possible route to the molecular hydrogen to a w-olefin structure (B) is permitted (22) ... 

Another observation that is difficult to reconcile with a mechanism of topside addition from adsorbed molecular hydrogen is the uniquely high yields of trans isomers obtained with palladium catalysts, i.e., about 85% frana-decalin from either Ai- -octalin or A i -octalin. Palladium, of all the transition metals, is the one deemed most likely to dissociate adsorbed hydrogen, and therefore least likely to involve molecular hydrogen in the saturation mechanism. On the other hand, palladium is one of the most effective transition metals for olefin isomerization and could isomerize A > -octalin to the thermodynamically unpreferred but rapidly saturating A > -octalin. 

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