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Hydrogenation of Alkenes with Metal Catalysts

Hydrogenation of Alkenes with Metal Catalysts: Mechanism

Hydrogenation of alkenes proceeds through several stages. In order to allow the educts to react, hydrogen has to be activated by the catalyst first. Hydrogen as well as alkene are being fixed to the surface of the catalyst where activation of both the π bond of the alkene and the σ bond of hydrogen takes place. Only after H atoms have been transferred to the alkene can the product (alkane) separate from the surface of the catalyst.

Fig.1
Schematic drawing of the mechanism of the platinum-catalyzed hydrogenation of alkenes

2D animation: Mechanism

2D animation: Isomerisation

Alkenes exhibit different reactivities in this reaction. Generally, cis alkenes react better than trans alkenes. Additionally, the number and size of substituents influence reactivity. Monosubstituted alkenes react the best. Because of steric hindrance, the worst reactivity is observed with alkenes possessing four substituents at the double bond.

Fig.2
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