How does hydrohalogenation mechanisms work?
May 28, 2016
It is basically an acid-catalyzed monohalogenation. I will use hydrobromic acid as an example.
- 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.
- 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).
- 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.
#"X"^(-)#can attack as a nucleophile and bind to the more-substituted carbon, as per Marknovnikov addition.