Orbital Diagram:6-atoms- 1,3,5-hexatriene: Videos & Practice Problems

Understanding molecular orbital diagrams for hexatriene involves recognizing the arrangement of six atomic orbitals and six π electrons. The process includes filling in bonding and antibonding molecular orbitals, ensuring symmetry and proper node placement. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are identified, with Psi 3 as HOMO and Psi 4 as LUMO. This stability arises from the conjugation of electrons into bonding orbitals, enhancing molecular stability while avoiding non-bonding orbitals.

Drawing MO Diagrams

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

Here’s what students ask on this topic:

What is the molecular orbital diagram for 1,3,5-hexatriene?

The molecular orbital diagram for 1,3,5-hexatriene involves six atomic orbitals and six π electrons. These orbitals combine to form six molecular orbitals: three bonding and three antibonding. The bonding orbitals are filled first, followed by the antibonding orbitals. The highest occupied molecular orbital (HOMO) is Ψ3, and the lowest unoccupied molecular orbital (LUMO) is Ψ4. Proper node placement and symmetry are crucial for accurate representation. The stability of 1,3,5-hexatriene arises from the conjugation of electrons into bonding orbitals, enhancing molecular stability.

How do you determine the HOMO and LUMO in 1,3,5-hexatriene?

To determine the HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) in 1,3,5-hexatriene, you first need to fill the molecular orbitals with the six π electrons. The electrons fill the bonding orbitals first. The HOMO is the highest energy orbital that contains electrons, which is Ψ3 in this case. The LUMO is the next higher energy orbital that does not contain electrons, which is Ψ4. Identifying these orbitals is crucial for understanding the molecule's reactivity and stability.

Why is symmetry important in drawing molecular orbitals for hexatriene?

Symmetry is important in drawing molecular orbitals for hexatriene because it ensures that the molecular orbitals are correctly represented, which affects the placement of nodes and the overall stability of the molecule. Symmetrical orbitals allow for proper conjugation of π electrons, leading to more stable bonding interactions. Asymmetrical orbitals can result in incorrect node placement and less stable molecular structures. Using symmetry helps in visualizing and predicting the behavior of the molecule more accurately.

What role do nodes play in the molecular orbital diagram of 1,3,5-hexatriene?

Nodes play a crucial role in the molecular orbital diagram of 1,3,5-hexatriene by indicating regions where the probability of finding an electron is zero. The number of nodes increases with the energy level of the molecular orbital. For hexatriene, the nodes help differentiate between bonding and antibonding orbitals. Proper placement of nodes ensures the correct representation of the molecular orbitals, which is essential for understanding the molecule's electronic structure and stability. For example, Ψ1 has no nodes, Ψ2 has one node, and so on, up to Ψ6 with five nodes.

How does conjugation affect the stability of 1,3,5-hexatriene?

Conjugation significantly affects the stability of 1,3,5-hexatriene by allowing the π electrons to delocalize over the entire molecule. This delocalization lowers the overall energy of the molecule, making it more stable. In the molecular orbital diagram, this is represented by the filling of bonding orbitals with electrons, which increases stability. The absence of electrons in antibonding orbitals further enhances this stability. Conjugation also affects the molecule's reactivity and electronic properties, making it an important concept in understanding hexatriene's behavior.