BRAINCAKEElectrophilic Addition of Hydrogen Halides
Hydrogen halides add to alkenes by the same electrophilic addition mechanism as bromine, with one difference in how the electrophile arises.
The H-Br bond is already polar: bromine is more electronegative than hydrogen, so the molecule has a permanent dipole, Hδ+-Brδ−. The δ+ hydrogen atom is the electrophile. (With Br2, the dipole has to be induced by the alkene.)
Mechanism for ethene + HBr
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Key terms in this lesson
- heterolytic fission
- The breaking of a covalent bond in which one atom takes both electrons, forming a positive and a negative ion.
- carbocation
- A positively charged carbon ion formed when a carbon atom loses a share in a bonding pair of electrons.
More in Alkenes
- Addition of Hydrogen Halides
- Electrophile
- Nucleophile
- Electrophilic Addition Mechanism
- Unsymmetrical Molecules
- Addition Polymerisation
- Identifying the Monomer
- Identifying the Repeating Group
All 19 lessons in Alkenes · All Edexcel AS-level Chemistry topics