Hydrogenation of Alkenes to give Alkanes

by James

Description: In the presence of a metal catalyst such as palladium, hydrogen will add to alkenes to give alkanes.

Notes: Many other metal catalysts can be used, such as platinum (Pt), nickel (Ni), or Rh (rhodium)

Examples: 

Notes: Note that the stereochemistry of addition to the alkene is syn (see the second example). Furthermore note that deuterium (the heavy isotope of hydrogen) can also be used instead of hydrogen. It works exactly the same way!

Mechanism: For the purposes of Org 1/ Org 2 the exact mechanism of this reaction is generally not considered important. However it does follow the following sequence: hydrogen and the alkene are both adsorbed onto the surface of the metal, and the hydrogen-hydrogen bond is broken. Then, both hydrogen atoms are delivered syn to the alkene.

Notes: 

 

{ 2 comments… read them below or add one }

Stephen Hamilton

Hey love this site, it’s an amazing resource. One suggestion though in the first example is to add the other hydrogens rather than just draw lines–they can be misconstrued for methyls which of course they’re not. Super super minor. Anyway great site!

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Camie Parsons

I wish my teacher agreed that the specific mechanism is not necessary. Any way you could show it?

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