For which reactions do we use markovnikov’s rule versus anti-markovnikov’s rule? (Regardless of the rule, the preferred reaction proceeds through the most stable cation or radical on the most substituted carbon. It requires the least substituted carbon of the C=C bond to be attacked. So, when the attacking particle is hydrogen (such as H+ in acid-catalyzed hydration or hydrohalogenation) or something that will become hydrogen later (Hg(OAc)2 in mercuration followed by reduction, the reaction goes by Markovnikov rule. If the least substituted carbon is attacked with something else (Br. in free radical hydrobromination) or Boron in hydroboration followed by oxidation, the reaction goes against Markovnikov rule - GS).
