Depto. Química Orgánica

ELECTROPHILIC ADDITION OF HALOGENS TO ALKENES

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15/07/2017
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The "pi" cloud of the double C=C bond can induce the heterolytic cleavage of the bromine molecule, giving rise to an intermediate with the structure of heterocyclopropane
(halonium ion).

The cyclic intermediate is opened by the halide counterion, leading to a vicinal dihalo derivative of anti stereochemistry.
Image The reaction is only of practical use for Cl2 y Br2.
Image Click on this box to realize the strong similarities between the aperture of the halonium ion and a protonated epoxide...
The halonium ion, once it is produced, can be captured with all sorts of nucleophiles:
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If the nucleophile is water or alcohols, one gets halohydrins or haloethers, respectively.

This is an excellent way of functionalizing two carbons in one shot.
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