Here the alkene goes through a transfer of electrons as well as atoms, an example
of reduction. Oxidation is always accompanied by oxidation and although the metal
is not formally oxidized, its ease of access to oxidative steps allows the reaction to take place. Here,
the alkene gains bonds to hydrogen and clearly is reduced.
Since there are electrons being transferred, we cannot draw reaction paths very easily. There is still a useful
picture that explains the chemistry of this reaction quite well. Most chemists imagine that the H-H on the metal
surface is synchronously joined to the carbons of the double bond.
Hydrogenation, the reaction of hydrogen gas with alkenes, is most famous in the saturation of some unsaturated fats.
The unsaturated fats tend to be cis alkenes which cause their structure to be kinked. This kink causes the fat to
be an oil. In order to get this molecular kink out of the molecule, we hydrogenated the fat causing the surface area
to be more regular and the melting point of the fat is raised. Triolein is a triacylglycerol which is a liquid oil.
Tristerin is a triacylglycerol that is solid. Not all double bonds get reduced in this process and some of the double
bonds are isomerized to the trans isomer, which has a more regular shape and contributes to the solidifying of the oil.
However, the trans alkene is metabolized differently than the cis and has been linked to raising the amount of cholesterol
in the body, raising the danger of heart disease.
