Key Concepts—Alkenes

A reagent XY adds to a double bond in one of three different ways  

Anti addition occurs in halogenation and halohydrin formation. 

Carbocations are formed as intermediates. Carbocation rearrangements are possible. Markovnikov s rule is followed. H bonds to the less substituted C to form the more stable carbocation. Syn and anti addition occur. 

Bridged halonium ions are formed as intermediates No rearrangements can occur. 

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