||Chapter 6: Reactions of Alkenes: Addition Reactions
Reaction of Alkenes
with Hydrogen Halides
Reaction type: Electrophilic Addition
- When treated with HX alkenes form alkyl halides.
- Hydrogen halide reactivity order : HI > HBr > HCl
> HF (paralleling acidity order).
- Regioselectivity predicted by Markovnikov's
"For addition of hydrogen halides to alkenes, the H atom adds to the C with
the most H atoms already present"
- Reaction proceeds via protonation to give the more stable carbocation
- Not stereoselective since reaction proceeds via planar
- For HBr is usually used in the dark and under an inert
atmosphere since care must be taken to avoid the formation of radicals when
an alternate mechanism occurs.
| MECHANISM FOR REACTION OF ALKENES
An acid/base reaction. Protonation of the alkene to generate the more
stable carbocation. The π electrons act pairs as a Lewis base.
Attack of the nucleophilic bromide ion on the electrophilic carbocation
creates the alkyl bromide.