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Hydrogenation of Alkenes

Addition of X2 to Alkenes

Halogenation and hydrogenation are examples of the addition of X2-type molecules to alkenes.

One might assume that the reaction mechanism of the addition of halogens to alkenes is very similar to that of the addition of hydrogen. However, the mechanisms are completely different as shown by the stereochemistry of the addition products. Hydrogenation is a syn addition, whereas halogenation is an anti addition. Additionally, catalysts are required for hydrogenations, while halogenations with chlorine or bromine, for example, occur spontaneously.

Fig.1
X2 addition

Exercise

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