This is an indentical mechanism to halogention, except with water as the nucleophile in the second step. Why would water prefer to react as a nucleophile over a halogen anion? Let’s find out.
General properties of halohydrin formation.
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Now I want to talk about a reaction that's so similar to hallucination that a lot of people get it confused with halogen Nation. It's just a little bit different because in this case, we're gonna be adding a halogen in the presence of water to a double bond. And this reaction is gonna be called a halo hydrant formation. Okay, so let's go ahead and get started. Basically, the general reaction is that I still have my double bond. I still have my diatonic halogen. The only difference is that I'm running this reaction in the presence of water instead of an inert solvent, I actually have water present. What that means is that the water is gonna wind up interacting and my end product is going to give me an alcohol on one side and a halogen on the other. This molecule right here is called as a functional group. It's called a halo hydrant. Okay, so let's go ahead and talk about the actual mechanism. The intermediate is once again gonna be abridged ion, just like before. The stereo chemistry is gonna be anti just like before, because any time you're opening up a three member ring, you're going to wind up getting anti products, and my product is gonna be a halo hydrant. Okay. Are there gonna be rearrangements? Nope. Okay. So no rearranging because there's no Carbonell. Whoa. Said that completely wrong. No carbon cat ion. And then finally, this actually will have Markov Nankov, um, re geochemistry. Because now I am adding two different things. So now I do have to be aware of which one goes on the more comic offside and which one goes on the ante. Markov Nick offside. But overall, we would say this is a Markov Nick Aww reaction because it's driven by the stability off the intermediate, okay?
Opening of 3-membered intermediates/molecules always results in anti-addition.
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So let's just go ahead and get started. The reaction is really straightforward. What I've got here is I've got the same situation where I've got a double bond and I've got a diatonic halogen and I've also got water. Let's just say so. I've also got water. Okay, which of these is going to react with my double bond? Well, water by itself doesn't really do anything to double Bond. You know, if I had water and acid, that would be different. Okay, but this is just water by itself. So you can't really react water in a double bond. But we know that we can react a diatonic halogen. So I'm gonna draw my three arrows once again where the X is making a bridge to the double bond. And it's also kicking out one of the exits as a leaving group. What this is going to give me is a bridge ion called polonium ion once again. And now we just have to figure out what's the nuclear file that's gonna do the backside attacker, The nuclear click attack of this rain. Okay, so basically, I got to nuclear files. I've got xnegative just like before, when we're talking about College nation. We've got the Xnegative just like before. Nothing has changed. But now what I also have is I've got some water lying around now of these two different species. Which of them do you think is gonna be the stronger nuclear file, the Xnegative or the water? What do you think? I've actually asked you as a question like this before for another mechanism. The answer is that the xnegative is gonna be much stronger. In fact, Xnegative is one of the best nuclear files around. Water is kind of like a because Xnegative has a negative charge. Water is neutral. So we would expect Xnegative to be a lot stronger. So why wouldn't I just get the Xnegative attacking and get hydrogenation reaction before? Well, the answer is that I will. Some of that actually will happen. Some of the xnegative will attack and I will get hallucination. But that's not gonna be what happens to the majority of the time. The majority of the time this bridged ion is so unstable that it's going to react with the first nuclear file that it encounters. Even if it's not the strongest. And what if I have once again how about if I have, ah, billion times more? How do I have a billion times more off the water than if I that I have of the Xnegative? So what if there's waters everywhere and there's only a few ex negatives? Okay, what's gonna wind up happening? What's gonna wind up happening is that even though the xnegative is stronger, the water is just gonna have an advantage because there's a lot more of it around. Because when I planned out my reaction, I used a little bit of diatonic halogen and I put a lot of water in there. Okay, so what that means is that in the second step, even though the xnegative is more stable is more nuclear Filic, my water is gonna wind up attacking the most substituted side. Does that make sense? Because there's just a whole lot more of it around now for this water. Is it gonna attack? The more substituted with less substituted. It's still gonna attack the more substituted side because that's the one with the most positive character I remember. The water has the electrons on it, so I go ahead and I make that bond. I break that bond. And what that's gonna give me is a major product. That is a halo hydrant. So if my water adds to the front, then that means that my ex is gonna add to the back. Okay? And that means that if my water was in the front, then my metal group would also be towards the back. Okay. Now, is this my final product? No. I still have one more step, Unfortunately, because I added water, so I need to de Protein eight. Right. I need to get rid of that age. What can I used to get rid of one of those ages? I could use the xnegative. So I'm gonna use the xnegative in this last step to pull off in h and give the electrons to the Oh, So now what I'm going to get is a product that looks like this. A market nick off alcohol and an anti Markov Nankov halogen. That's anti. Do we have Karl centers here? Yep. So we have to draw both an anti MERS. The other an anti mur would be that the water attack from the bottom. The method is now at the top And that means that my ex is now at the top. And these would be a race emmick mixture, because I really have no clue which side it came from. Does that make sense, guys? So I hope that you guys were able to see the similarities between halogen nation and the halo hydrant formation. The only difference is that I've got a lot of water around. So when that second nuclear for, like, attack, water is going to do the attack instead of the xnegative. All right, so let me know if you have any questions on that. But if not, let's go ahead and move on.
1. Electrophilic Addition
2. Nucleophilic Substitution (SN2) and Deprotonation