Additions via Carbenium Ion Intermediates

In Section 3.5.1, it was mentioned that Br2 and Cl2 form resonance-stabilized benzyl cation intermediates with styrene derivatives and that gem-dialkylated alkenes react with Br2 hut not 

Preparatively, it is important that mineral acids, carboxylic acids, and terf-carbenium ions can be added to alkenes via carbenium ion intermediates. Because of their relatively low stability, primary carbenium ions form more slowly in the course of such reactions than the more stable secondary carbenium ions, and these form more slowly than the even more stable tertiary carbenium ions (Hammond postulate ). Therefore, mineral and carboxylic acids add to unsymmetrical alkenes regioselectively to give Markovnikov products (see Section 3.3.3 for an explanation of this term). In addition, these electrophiles add most rapidly to those alkenes from which tertiary carbenium ion intermediates can be derived. 

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