"We can see from these examples that, if the carbon atoms participating in the double bond are not equally substituted, the proton from the hydrogen halide attaches itself to the less substituted carbon.As a consequence, the halogen ends up at the more substituted carbon. This phenomenon, referred to as the Markovnikov rule,can be explained by what we know about the mechanism of electrophile additions of protons to alkenes. The key is the relative stability of the resulting carbocation intermediates. (...) On the basis of this analysis, we can rephrase the empirical Markovnikov rule: HX adds to unsymmetric alkenes in such a way that the initial rotonation gives the more stable carbocation."