9. Alkenes and Alkynes
Zaitsev Rule
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the last thing I want to do is I just want to show you guys with an energy diagram that I'm going to sketch up really quick what these words mean between thermodynamic and kinetics because this is going to come up more in Orgo 1 and in Orgo 2. So I just want to show you guys, remember that you have an energy diagram and the way that it works is that you have some kind of, you know, spontaneity here and you have a reaction coordinate here where basically at the end I have a double bond and at the beginning I have just my alkyl halide plus the nucleophile. Okay? So what I want to show you guys is that this is a concerted reaction, so it all happens at the same time. So I'm only going to have 1 hump, I'm going to have 1 transition state. Remember that e2 just has a transition state. The thing is that what it looks like, what the kinetic versus the thermodynamic energy diagrams look like are going to be different. So for the thermodynamic one, I'm going to start up here at this energy level. I'm going to pass through a pretty big, I'm sorry, a pretty big hump in energy and then I'm going to gain a lot of energy at the end because my double bond is overall going to save me some energy. So that's what the elimination product would look like for the first one. Okay? Are you guys following so far? Cool. Now for the second one, what I would find is that my energy level is at the same place at the beginning. Okay, so it's right here. I'm still there's my kinetic pathway. But it turns out that for the kinetic pathway, I'm going to have a much lower activation energy, but then I'm also going have a much lower gain in stability. Okay? So what you can tell is that check out the enthalpy for a second or the spontaneity. Okay? Overall, I'm going to gain I'm sorry, it's supposed to be change I'm going to gain I'm sorry, it's supposed to be change in Delta g. Okay? Overall, my product for the red, for the Zaitsev product is going to be overall more stable at the end. I'm going to gain more delta g or more free energy by going in that direction than by going in this direction. Is that making sense so far? So basically the red one is overall more stable than the green. Okay? But what we're also going to notice is that the activation energy of the first one is much higher and the activation of the second activation energy of the second one is much lower. Okay? So the green is what we would call kinetic control. Kinetic control kinetic control basically means that all I'm looking at is the one with the lowest activation energy. Okay? I'm saying whichever one is the easiest one to form, that's the one that's going to be favored. Okay? Whereas thermodynamic control, I'm just going to put here thermal, is the one that looks at the overall lowest delta g. The one that changes, that gets the most free energy at the end, that's the most stable at the end, that's going to be the one that I favor. Okay? And that's the difference between Zaitsev and Hoffman. Basically, Zaitsev is thermodynamic control, where all I care about is the stability of the end product. Okay? Whereas, Whereas, Hoffman is going to be kinetic control because all I'm going to care about is the one that's the easiest to form or the one with the lowest activation energy. Is that difference kind of making sense? Now the reason I'm telling you guys this is because this is going to come up later when we talk about other reactions in Orgo 2. There's going to be kinetic control and thermodynamic control and it's going to be the same kind of principle where I'm looking at either the stability beginning. Alright. So I hope I didn't confuse you guys here. I just really want you guys to understand the difference between and how one is thermodynamic and one is difference between Zaitsev and Hoffman and how one is thermodynamic and one is kinetic. Alright. So let's go ahead and do some practice problems based on Zaitsev's rule.
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