How does hydrohalogenation mechanisms work?

1 Answer
May 28, 2016

It is basically an acid-catalyzed monohalogenation. I will use hydrobromic acid as an example.

  1. For an alkene, which I presume is your substrate, the alkene would have the capability to donate electrons from its #pi# bond to polarize the #"H"-"X"# bond, where #"X"# is a halogen.
  2. That changes the molecule's electron distribution so that we have #stackrel(delta^(+))("H")-stackrel(delta^(-))("X")#, which then leads to the acquisition of a proton from the hydrohalogenic acid onto the less-substituted carbon (the one with more hydrogens).
  3. The formation of a carbocation intermediate occurs as a result. This intermediate is the more stable carbocation, which is usually the one with more alkyl groups around it.
  4. Then, #"X"^(-)# can attack as a nucleophile and bind to the more-substituted carbon, as per Marknovnikov addition.