In this video, we're going to learn how to draw the molecular orbital diagrams of 6-atom conjugated systems, usually hexatrienes. Let's go ahead and get started. As we know well, conjugated polyenes are famous for their ability to resonate, and we can explain that resonance using molecular orbitals. So the primary purpose of this page is to apply the rules of building molecular orbitals to a 6-atom system. It does get more complicated. We are going to have to think a little bit more about this, but we're doing it together, so it's all going to be okay. Let's talk about what we do know, which is that there are 6 atomic orbitals, 6 pi electrons, and 6 molecular orbitals. Alright? And I've gone ahead and, as always, filled in the first one for you so that we know what we're dealing with. It's also the easiest one, and then we're responsible for the rest. Okay, so what do you think is the best place to start? Let's go ahead and fill in the first orbital and the last orbital for all of these. I'm going to fill in 1st, 1st, 1st, 1st, and 1st. Then I'm going to start flipping the last ones. Flip, flip, flip, flip, and flip. Cool? And if you guys don’t mind, I'm even going to do one more little cheat, which is I'm going to fill in size 6 already because we already know that size 6 is always just going to be every single orbital facing a different direction. So we can already fill that one in, just kind of like by definition, we're used to this by now. Cool? So that means that all we really need to worry about are these four in the middle for sides 2 through 5. Okay? Let's also just remind ourselves how many nodes we're supposed to have. So it's supposed to start at 0 and then 1, 2, 3, 4, and 5. We can also fill in the nodes for 5, we know that it's just going to be between every single orbital. Cool. The hard part is the others. Okay, cool. So let's start with side 2. I don’t think this one’s going to be too challenging. Let's look at this together. We need to put in one node, where do you think is the best place? Let me know when I'm getting closer. Yeah, right here, right? So this is it. Let's put in our node, and that's it. That's totally symmetrical. That's where you’d want to do it. Okay? Let’s go to side 3, but for 2 nodes. It’s actually not that hard. This one’s pretty straightforward. It’s just going to be here and here, right? Just like that. That makes sense; it's not really that difficult. Okay, now we get to side 4 and it's tricky enough so that I think it is appropriate for me to actually use an obscure rule that was in my molecular orbital rules. Remember that rule said that if in doubt, if
16. Conjugated Systems
Orbital Diagram:6-atoms- 1,3,5-hexatriene
16. Conjugated Systems
Orbital Diagram:6-atoms- 1,3,5-hexatriene - Video Tutorials & Practice Problems
Conjugated polyenes (i.e. hexatriene) are famous for their ability to resonate. Here we will explain that resonance using molecular orbitals.
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concept
Drawing MO Diagrams
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