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Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

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16. Conjugated Systems

Orbital Diagram:Excited States

Conjugated molecules have the ability to absorb light energy and kick electrons up to a higher energy state. This may have an effect on our HOMO/LUMO orbitals. 


Ground vs. Excited States

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Hey, guys, in this video, we're going to discuss a very unique phenomenon that happens when a conjugated molecules is exposed to light. Let's get started. So guys conjugated molecules have the ability to absorb light energy and turn convert that light energy into mechanical energy by kicking electrons up to, ah, higher energy state. And when this happens, that means that your homo and limo orbital's are going to change, because now you have electrons resting, indifferent orbital's than they initially work in their ground state, and this actually will have big implications on reactivity. But we're gonna get to that later because right now you don't even really know how Homo and Momo react. But later on we talk more about how Homo and we will react with each other. The fact that you can excite electrons to a new home Oh, and limo really will be important. Okay, so here's an example. 13 Beauty dying is irradiated with pro with photons exciting an electron up toe. Ah, higher energy, Molecular orbital. So, photons or light, you're shining the light and we're exciting. An electron. Okay. Predict the identity of the Homo and Lou Mo orbital's after irradiation. So what we would start off within the ground state guys is just four pi electrons, right? Because you have to hear you have to hear four pi electrons and I would fill them in order of ALF about principle 1234 And I already have the homo and limo written out for us. Homo highest occupied aside to low, lowest unoccupied aside three. And that's what we're used to. This is what the molecule looks like in its ground state. But if you shine enough light on this molecule, what's gonna wind up happening is that it absorbs one of the photons, and it's going to basically convert that energy into an electron being kicked upto a higher energy state. So what it's gonna look like after irradiation is this? So let me just get out of the way here. These two electrons stay the same. But now I only have one electron here and now I have one electron here. Isn't that interesting? We're basically What we just did is we just took one of the electrons and moved it up here. Now I know that before I had an up spin and the down spin, and now I'm just making it to up spins. That doesn't matter. Don't worry about whether it's up spinner down spin that you don't need to worry about that For any of predicting home own limo. All you need to worry about is which orbital it's in. So that means that which orbital is now the homo, the homo is now Cy three, and which orbital is now the loom? Oh, the loom Oh is now side four. So, guys, this is very important because this means that we can use light to manipulate which orbital's react as a homo and which orbital's react as a loom. Oh, cool, Awesome. So that's it for this video. Let's move to the next one.

4-Methylbenzylidene camphor (4-MBC) is used by the cosmetic industry for its ability to protect the skin against UV-B radiation. Circle the part of the molecule that you theorize is responsible for its effects on UV light.

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