Markovnikov's Rule: In electrophilic addition of HX to unsymmetrical alkene, H adds to the carbon with MORE hydrogens (forming the more stable carbocation).

Mechanism: H+ attacks pi bond → carbocation intermediate (more substituted = more stable) → X- attacks carbocation → product.

Anti-Markovnikov (Kharasch effect): HBr + R-O-O-R (peroxide) → radical mechanism.

• Br· adds to less substituted carbon (forming more stable radical on more substituted carbon)
• H· transfers from HBr to the radical
• Works ONLY with HBr: HCl bond too strong for propagation; HI gives endothermic propagation step

Hydroboration-oxidation: Also anti-Markovnikov but via concerted 4-center mechanism (not radical). B adds to less substituted C (less steric), then oxidation replaces B with OH.