All About Alkenes

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THE MECHANISM REACTION OF ALKENES

1) Hydrogenation
2) Halogenation
3) Hydrohalogenation

THE HYDROGENATION OF ALKENES
Hydrogenation is an addition of hydrogen (H2) to unsaturated organic compounds in the presence of catalyst such as platinum, nickel and palladium to form alkenes. It includes the manufacture of margarine from animal or vegetable fats and oils.

THE HALOGENATION OF ALKENES
Halogenation is the addition of halogen atoms to a π-bond system.
The reaction of a halogen with an alkane in the presence of ultraviolet (UV) light or heat leads to the formation of a haloalkane (alkyl halide).
Experiments have shown that when the alkane and halogen reactants are not exposed to UV light or heat, the reaction does not occur. However, once a reaction is started, the light or heat source can be removed and the reaction will continue. The mechanism of the reaction explains this phenomenon.

THE HYDROHALOGENATION OF ALKENES
A hydrohalogenation reaction is the addition of hydrohalic acids like hydrogen chloride or hydrogen bromide .
Unlike halogens, hydrogen halides are polarized molecules, which easily form ions. Hydrogen halides also add to alkenes by electrophilic addition.
The addition of hydrogen halides to asymmetrically substituted alkenes leads to two products.
The major product is predicted by the Markovnikov rule, which states that when a hydrogen halide is added to an asymmetrically substituted alkene, the major product results from the addition of the hydrogen atom to the double-bonded carbon that is attached to more hydrogen atoms, while the halide ion adds to the other double-bonded carbon. This arrangement creates a more stable carbocation intermediate.

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January 27, 2010 - Posted by | Reactivity Of Alkenes, Uncategorized

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