Anti-Markovnikov's rule predicts the opposite regiochemistry of Markovnikov's rule in certain reactions, especially in free radical additions.
1.Markovnikov's Rule:
In the addition of a protic acid (HX) to an unsymmetrical alkene, hydrogen (H) attaches to the carbon with more hydrogen atoms, while the halide (X) attaches to the carbon with more substituents.
2.Anti-Markovnikov's Orientation:
In free radical conditions, the hydrogen adds to the more substituted carbon, while the halogen (or another group) attaches to the less substituted carbon.
This occurs due to the stability of the radical intermediate rather than carbocations.
Example:
The hydroboration-oxidation of alkenes (BH₃ followed by H₂O₂/NaOH) adds BH₃ in an anti-Markovnikov manner.
In free radical additions, the Kharasch effect (addition of HBr in the presence of peroxides) results in the bromine adding to the less substituted carbon.