Base-Catalyzed Alpha-Halogentation - Video Tutorials & Practice Problems

Base Catalyzed

This is in contrast to the base catalyzed mechanism. In the base catalyzed mechanism, you may yield polyhalogenation. The reason is you're basically going to yield as much halogenation as you have alpha protons. The reason being that in a base catalyzed mechanism, the Xs being there are just going to make it more reactive the second time. Let me show you. In a base catalyzed mechanism, imagine that I'm using OH^- and that I'm just forming an enolate right away. That enolate looks like this: negative charge. That negative charge can react with X₂ to this, to that. Go here, go there, and give me my halogen. But now when it sees that second equivalent of base, guess what's going to happen? Now we have a dipole pulling away, so it's going to be easier to put a negative charge there because the negative charge is going to be stabilized by the halogen. Therefore, we're going to replace every single halogen or every single hydrogen that was there. We'll replace all those alpha hydrogens with Xs and we're going to get polysubstitution. The only reason that I put "may yield," not "will yield" is that obviously, you need multiple alpha protons in order for it to get polyhalogenated. If you have only one, then you're only going to substitute once. But you can basically continue to react, continue to keep reacting until you're out of alpha protons. Interesting, right? Cool, guys. In the next video, I want to show you an application of alpha halogenation called the haloform reaction.

Provide the major product for the following reaction. 

• A.
• B.
• C.
• D.