Organic Chemistry

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Table of contents
16. Conjugated Systems

Orbital Diagram:5-atoms- Allylic Ions

3 and 4-atom systems aren't the only kinds of conjugated systems we will encounter. There are also 5-atom systems that we can draw molecular diagrams for. Let's take a look.


Drawing MO Diagram

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Alright, guys, in this video, I'm going to show you guys how to draw the molecular orbital diagrams for a five Adam conjugated system. Let's go ahead and get started. So, like Prepon eel ions, those three Adam Congregated systems five Adam conjugated systems have the ability to resonate reacting in multiple locations. Okay, same idea. Um, and regardless of the identity of the ion, no matter whether it's a positive charge or a negative charge or anything in between, you can explain the reactivity of the molecule using molecular orbital's. Okay, So what we're gonna do here is the number. One thing we're gonna do is we're gonna draw the molecular orbital's for a five Adam. Contrary system. Because guess what? It's a little bit confusing. And if we don't go through it together, you may not know how to do it. Okay, So predict the L CEO model off five carbon system. Identify the bonding, non bonding and anti bonding. Orbital's cool. So, guys, what we're basically saying here is that we don't know what type of molecule or what type of ion this is. It could be zero electrons, one electron or two. Okay, but that is going to go into the fifth atomic orbital, and we're gonna figure out what to do with that later. For right now, our main job is to fill in. What do the atomic orbital's look like? Okay, so I've already given you the five molecular orbital's. Now we just have to actually fill in the phases. Okay, So what do you think is a good place to go from here? Like, what's a good starting point? Let's go ahead and fill in the first atomic orbital in each and keep it exactly the same by the rules. By the way, the rules are not going to change it all. I'm just showing you how to apply them to a five Adam system. Cool. So then over here, we should probably start flipping the last one back and forth. Flip, flip, flip and flip. Not too bad. So the only ones who really have to decide are these three in the middle. Okay, Now we need to do is start putting in our notes just to remind ourselves we should have zero one to three and four notes. Okay. They have to keep increasing. So let's start off with our first one. Where do you think is the right place to put a note? If I can only put one, and it needs to be symmetrical, it needs to be here. Needs to be in the middle. Okay, so that's gonna be our first note. That means we're going to ignore that orbital. It's going to get deleted quotes. Let's go to To. Okay, So where can we put two nodes in a place that symmetrical? Where can we do it? So, guys, this is a little bit tricky, but it's gonna make sense when they say it. You actually have to put it on orbital too. And an orbital four. Right. That's the only way to keep it Symmetrical is to go on to orbital to and Orbital four. Which means that in this one we're gonna delete to Orbital's. Okay, cool. Let's go to the next one. So for the next one, we need to put in three. Where could we put in three. What do you think? So the place to put in three would be First of all, we definitely put one in the middle, right? Because the middle is it's an odd number. So you have to put one in the middle for sure. Okay. And then the other places that you would put it would be here and here. Okay, Now, those are the Onley really logical places to put it. And the reason is because let's say that you were put it next to the one in the middle. Well, then that would be very symmetrical. That would just be a bunch of nodes in one place, right? You want to keep it evenly space. And let's say that you were to cover up these notes here. Well, then, what would happen once again is that you have a lot of notes next to each other and then not a lot of notes here. So that's what we're trying to do is keep our nodes evenly spaced. So by evenly spacing it out, we would have knowed then Onley delete one and then note again. Okay, Cool. And then, finally, the last one should always be easy, guys, because it just means that every single position gets a note. Okay, So see how I hope. Like, the rules didn't change, but I hope that it helped seeing how I think about it, okay. And doing it together. So what that means is that now we're gonna fill in our other nodes. That means that this one is down and this one is up. That's our one phase change for this one. It's actually gonna be What would I draw? I only draw this up because the other two are deleted. Right? So for this one, I do a phase change up, ignore the middle, and then a phase change down. And then finally, for this one, they're all flipping cool. Awesome guys. So now we just filled in our molecular orbital's. And now we just have to put in the pi electrons into the orbital. So we know that for sure you would get to inside one you'd get to inside to, and whatever the identity of that fifth Adam is, whatever's in here is gonna go right here. Okay? Now what do we see? That's interesting about side three. What's the shape of Side three now, By the way, this is going beyond what the question was asking. But I just think it's a really cool application of what we know about molecular Orbital's. What are the places that sy three could react it only has three orbital's right. It only has Orbital's at position a position C and position E. Right. Notice that position B doesn't exist and position D doesn't exist. Okay, And that explains why whatever I on this is, let's say it's a plus charge that it can Onley resonate thio here and to hear because that's the Those are the only places where electrons could actually interact with other electrons because those are the only orbital's that do not have notes. Isn't that cool? Awesome. So you guys are becoming molecular orbital freaks. You guys were totally getting this. Now we do have Thio do our last part about the orbital's So guys, um, there's a little bit of notation that we're missing, right? So first of all, this is bonding. This is also bonding. Anything that's below the 50% mark is bonding. Anything that's above it is anti bonding. So that means this is anti bonding and this is anti bonding, right? And that also means that we should add stars here because these stars are missing, okay, and then what is Cy three? Cause it's right at that halfway points. Any time that you're at the halfway point that is actually considered non bonding, and it neither adds nor subtracts from stability. So the non bonding one is usually actually the reactive one. It's the one that can react with other ions and other molecules. And that's really where the fun stuff happens. It doesn't make it more stable. Toe have electrons there. It doesn't make it less stable. Toe have electrons there. It's just basically kind of like it's part. It's the It's the place where the reactions happen most of the time at the non bonding position. Cool, awesome is, and there's no special notation for it. Okay, awesome guys. So we're done with this problem. Let's move onto the next video.

Predict the molecular orbitals and identify the HOMO and LUMO orbitals of the following cation.

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