Question

How does hydrohalogenation mechanisms work?

Answer 1

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.