What is the mechanism of hydrohalogenation?

Hydrohalogenation = Addition of HX (HCl, HBr, HI) to an alkene.

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Mechanism (Step by Step)

1. Double bond attacks H⁺
   • The alkene has a π bond (electron rich).
   • This bond attacks the H⁺ from HX.
   • One carbon gets the hydrogen.
   • The other carbon becomes a carbocation (C⁺).
   • This step follows Markovnikov’s rule (H goes to carbon with more hydrogens).

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2. Carbocation formation
   • The more stable carbocation forms (tertiary > secondary > primary).
   • That’s why Markovnikov’s rule works.

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3. Nucleophile attack
   • The halide ion (X⁻, e.g., Cl⁻, Br⁻, I⁻) attacks the carbocation.
   • This makes the final product: an alkyl halide.

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Example:

Propene + HBr →

• Step 1: Double bond attacks H⁺ → carbocation forms on middle carbon.
• Step 2: Br⁻ attacks carbocation → product is 2-bromopropane.

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In short:

1. Double bond grabs H.
2. Carbocation forms (stable one).
3. Halide attaches to carbocation.