The hydrogenation of alkynes and alkadienes

The metal-catalysed hydrogenation of multiply unsaturated hydrocarbons is, of necessity, more complex than that of monoolefins. The problems encountered in alkyne and alkadiene hydrogenation are essentially similar and it is appropriate, therefore, that the two systems are considered together. 

A further problem arises when one considers the hydrogenation of alkynes and alkadienes containing four or more carbon atoms. In such cases, it is possible that the intermediate olefin may be formed in more than one isomeric form. Hence, the stereospecificity of the hydrogenation must be considered and attempts made to explain the observed stereospecificity in terms of the mechanism (see Sect. 4.3). 

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