Anti-Markovnikov addition is the opposite of Markovnikov’s rule.
It says:
When HX (like HBr) adds to an unsymmetrical alkene in the presence of peroxides (ROOR),
- Hydrogen (H) goes to the carbon with fewer hydrogens.
- Halogen (X) goes to the carbon with more hydrogens.
Example:
Propene (CH₃–CH=CH₂) + HBr (with peroxide) →
- Normally (Markovnikov): H goes to CH₂ → product is 2-bromopropane.
- With peroxide (anti-Markovnikov): H goes to CH → product is 1-bromopropane.
In short:
- Markovnikov → “the rich get richer” (H goes to carbon with more H).
- Anti-Markovnikov → “the poor get richer” (H goes to carbon with fewer H).