Benzyne

Alright, guys. So at this point, we've learned about two different addition elimination mechanisms for benzene. One is Elektra Filic and one is nuclear Filic. But it turns out that there is another form of nuclear filic substitution out there. But this one is an elimination, then addition pathway, It's weird. So this is called the benzene pathway. Okay, so it turns out that benzene can progress through an elimination addition pathway, but it's gonna make a very unstable intermediate That unstable intermediate is called on a Rhine or benzene because it literally has a triple bond within the ring. Imagine how unstable it is to have a triple bond. Remember, Trip wants wanna have ah, bond. Angle of what, 180 degrees. And it's gonna be forced into 123 bond angle on that cyclo hexane, so it's gonna suck. OK, um but it can happen, and this is actually a way that we make an a lien. So let me show you guys kind of the mechanisms that we've learned so far and how benzene benzene is similar and how it's different. It's mostly just different. So you guys gonna go through this really fast. You know that for A s, I can add first, and then it can eliminate. Okay, so we get our addition and elimination through an electro file, so we call, it s We know that for Snr I can also add first. But the way we add is actually through a nuclear feel like attack, Okay? And then we eliminate using the same and I am okay, so we also get addition elimination. But this one is nuclear Filic. So s n a r. Well, the air and pathway or the benzene pathway is much, much different because what happens in the benzene pathways that we have to actually eliminate first, how do you eliminate from a benzene what you literally have to do e to you literally have to do, um, a beta elimination on the spending so you would grab one of the H is with a strong base. You just a strong base and you would literally do the three arrows four and e to attack. I would grab the H, make a triple bond and kick out the X. What this is going to make is a very unstable benzene. Okay? Again. Also called Aaron, Because Aaron is a benzene rings, so Ah, Benzene. Intermediate. Okay, so extremely unstable. Okay, so now we have toe add okay. And the way we add is with the conjugate base or the conjugate acid, the conjugate acid, um now can be used toe add to the benzene. The mechanism is a little weird, but just bear with me. What we're gonna do is we're gonna take our conjugate acid. I'm gonna attack one side of the triple bond and kick those electrons down to form an an I am. So what this is gonna form is another intermediate That looks like this. I've got my benzene is back now with a negative charge. And then I've got B h. For now, be has a positive charge because that's one too many bonds. Okay, And then to finish this up, this negative can do an intra. I could basically a proton exchange, and it can finally grab the H and we can get our substitution. Okay, So that substitution Damn, it took a long time. It's kind of weird pathway, but we got a base to switch out for a halogen. Okay, so what? I wanted to show you guys is how we can use this to make, um, an anally. Okay, so how could we make an anally in using this mechanism? Well, the base that we use this very typical reaction is N h two negative. A very strong base. Okay. And we're going to do an elimination first. So we're gonna take in age. We're gonna do a beta elimination. This is going to give me my Ben sign. Cool. So there's my Ben sign. Awesome. So what happens next will notice that now I actually have. You know, my my base is NH three, and I still have a loan period. Still somewhat nuclear feel like Okay. So I can use the conjugate to attack or add toe one side and kick electrons down to that one to that side of the double bond. So what I'm now going to get is a molecule. Looks like this. Oops. I wanna keep the drones in the same place and h way put the ages on the other side. N h two h positive and negative. Charge. Right. And then we do the proton exchange, and we're finally going to get what, guys? What? You just finally get the end of this is Anna lean. Okay, so this is actually a way to make an a lien. You can make an a lien using an N H two based on basically an arrow. Hey, lied. Okay, you start off with an arrow. Hey, Wide plus And each too negative can give us an alien. Crazy, huh? Awesome. So let's go ahead and flip the page.

when it comes to the benzene pathway. There's one more thing we need to learn about because so far all I showed you was benzene by itself. But what happens if that benzene is asymmetrical and has substitue INTs on it? How do we know which side of the benzene is going to get attacked? Well, it turns out that this is what we call benzene regio specificity, and there's actually trained for it. So let's learn it. So here's the issue. Let's say that we have the following Benzene Intermediate, right? And I'm at the point where my NH three is going to attack. We'll notice that now I've added an O age group. So if my NH three attacks from here, I would get a loan performing here and eventually going to get the NH too close to the O. H. Or if my NH three attacks here, I'm gonna get the loan performing here, and eventually my NH three will be meta to the O. H. So which one is right? So I just get a combination of products? Actually, no. The identity of where of the location of where it adds is based on the type of group that is next to the benzene. So, guys, I'm gonna explain the theory. But thankfully, memorizing is really easy because this follows the same trends that we've seen all throughout benzene chemistry, which is that a donating group is gonna favor the Ortho position and withdrawing group is gonna favor the meta position. So we remember how withdrawing groups are always meta directors and joining groups are Ortho para directors. Well, it's the same thing here, Okay? Except we're not gonna worry about pere because Pere doesn't even have of benzene on it. So I'm just worried about Ortho and Method Ortho Meta. So here's the theory behind it. Okay, notice that what I have here for O. H is actually a donating group, right? Okay. So if I have a donating group, that would put me into the bottom category here. Okay. When I have to form that negative charge, I have two different options. I could either form the negative charge here close to the donating group, or it could form the negative Intermediate. Lower away from it. Which one do you think is gonna be more stable? Having it closer to the donating or further further, guys. So what's gonna happen is that the NH three is gonna selectively pick the Ortho position just so that it could put the negative charge further away from the donating group. Okay, so that's why when you have an electron donating group or though substitution is gonna predominate, Okay, Now, the opposite is true of withdrawing group. So if I have a strong withdrawing group, then we want the negative charge to be as close to it is possible. So then that's gonna favor meta substitution. Okay, so you guys can totally know the theory, but you could also just memorize it, and that would be fine. Okay, So let's go ahead and do a practice problem now knows this is going to be kind of multi step synthesis. A lot going on. A few other re agents try to do your best. Notice that here you do have to worry about radio chemistry. So try to pick the right answer, and then I'll go ahead and I'll give you the right answer

Alright, guys. So first, let's just take care of the benzene pathway part and then we'll worry about the other agents. So it has to show the full mechanism. So we will. So we're going to do first is a beta elimination. We have to do it with that hydrogen because the other side doesn't even have a hydrogen. So I would do this. This and this. What that's going to give me is a molecule that now looks like this triple bond and 02 door one, door one. Okay, so now notice that we have a withdrawing group next to the benzene, meaning that when my NH three comes in tow attack, I'm going to attack at the meta position. Okay, so good job. I'm pretty sure most of you got that right. So now I'm going to get Oops. This is a withdrawing group. Okay, so now I'm going to get the intermediate. That looks like this N 02 Benzene, benzene, benzene. Negative. N h two h, positive. So now I'm gonna get a proton transfer, and I'm going to end this stage with mm nitro Angeline. Okay, so that's my product. Here. It's Metta Nitro Angeline. Perfect. So now I'm gonna react this benzene derivative with an e n 02 which what you guys think is going to do that's going to do to my benzene. Any ANO, too, is part of a die as, um, die as a pathway reaction. Okay, so if you haven't gotten here yet or if you don't remember it, you can look thes reactions up in the DIA. So section you can search, um, die Azzoni, um, reactions in the clutch curriculum in the clutch search bar. And it'll take you to their Okay, But if you haven't gotten here yet, then it's because you just you don't need to know this yet, so just don't worry about this particular part, Okay? So what that's going to do is it's on Lee going to react with the NH two because the nitro doesn't react with nitrous acid. That would give me the nitro remains untouched. But that would give me and drew one and a die as well compound. And that is going to react with my replacement reaction to give me my final compound, which would be nitro on one side and a scion oh, group on the other excellent guys. So sorry in the way. So the most important part here was the benzene pathway. That's what I'm concerned about. If you happen to not remember these re agents, it's not a huge deal Will practice them more in that particular section. Okay, but you guys did really well with benzene. Now you guys know three pathways, right? You guys know e A S S N a r and benzene. That's huge. That's pretty much all of the mechanisms that bans and undergoes. Okay, so awesome lesson. Let's move on to the next topic.

Which is the major product for the following reaction?

• A.
• B.
• C.
• D. No reaction

Which is the major product for the following reaction?

• A.
• B.
• C.
• D. No reaction