Alkynes contain two π-bonds, so when they are exposed to electrophiles, they do exactly what you would expect them to do:they react TWICE with them.
Halogens Add Twice to Alkynes
General properties of double addition reactions to alkynes.
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It turns out that all kinds can react with Hala Jin's ah, lot the same way that double bonds can, except for the fact that double bonds, remember, have one pie bond and triple bonds have to. So what that means is that some re agents that we exposed to al kind are actually gonna react twice, and that's what we're going to study right here. So basically, there's two different reactions that all kinds will react twice with. And these were gonna produce double addition products. That just means that anything I was expecting to get for my double bond, just double that. And that's gonna be my expected product for a triple one. Okay, Now, keep in mind if we have Carbo Catalans in any of these mechanisms, which we will that vinyl carbo cat ions. Now, remember what the word vinyl means. It means something directly on a double bond. That means a carb Acadian that looks like this. Okay, Vinyl carbo Catalans cannot easily rearrange. So what that means is that don't be thinking about shifts in these mechanisms because they're really just not gonna happen. Okay,
Keep in mind that for some of these reactions, vinyl carbocations will be created. While unstable, these cannot rearrage, so don’t worry about carbocation rearrangements when reacting with alkynes!
Double hydrohalogenation of alkynes.
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So let's go ahead and look into the first one. And the first one is a hydrology nation of an Al Qaeda. Now, ah, hydrology nation, remember, is just in h x with a triple bond. Okay, well, if I were to react at one time, I would expect to get on Markov. Nankov halogen. Okay, added. But it turns out that if you react this twice with al kinds, what you're gonna wind up getting is actually gem Die. Hey, lights. Okay, Now, remember that the word gem is stands for genital, and that means that they're both on the same carpet. Okay, so let's go ahead and see how this works. If I would react this with one equivalent, I would expect to get that the triple bond attacks the H kicks out the X. So I wind up getting a Carvell Catalan that looks like this with a positive charge here and in h here. Okay. And then that positive charge would grab, or I'm sorry the X would grab the positive charge, and I would get my intermediate my first product. Okay, but if I expose it to more than one equivalent, for example, let's say that exposed it to two equivalent total. Then it could react again. So then I could get this double bond attacking the age kicking out the X would I would wind up getting is a carbon county. And that looks like this where my ex is there, my h is there. And once again, I would get my ex. And now, by the way, there's two h is there, and then my ex would attack there again. So what? I would wind up getting as a product that looks like this where I have a five member ID ring with two exes in the Markov Nick off position. Okay, so it's the general daylight part, and that's amore comic off part. And then I would have to h is that came from my audition reaction. Okay, I know if you're wondering Well, what about that? Carbon shouldn't have three. H is Shouldn't it be ch three? Yeah, well, that h was always there, though, and that kind of looks messy. And it's going to redraw that that h was always there because that's the H that was originally on that triple bond. Anyway, I'm just saying that through this reaction we wind up adding H twice and ex twice. Does that make sense? I hope so. I hope that that flows. It's really not a complicated reaction, as long as you know what hydrology nation is, okay?