Markovnikov's rule or Markownikoff's rule started that in addition to polar reagent to unsymmetrical alkene the negative part of the polar reagent (Cl, OH, F etc) is attached to the carbon having the lowest number of hydrogen while the positive part of the polar reagent (H,Na,Mg,Al etc) is attached to the carbon having the highest number of hydrogen. The rule was postulated by Vladimir Markovnikov.