What I want to do is show you 2 3D versions of cyclohexane, and I want you guys to tell me which one you think is going to have the lowest heat of combustion. Alright? I haven't even taught you about cyclohexane yet, but I just want you guys to predict which one has the lowest heat of combustion. So go ahead and just like pause the video, and then when you're done thinking, also think: What does the lowest heat of combustion mean? So once you're done thinking, unpause the video.

Alright, so I'm pretty sure that you guys got that the lowest heat of combustion means the lowest energy and that lowest energy means most stable. Okay? So we're looking for the one that has the least amount of strain. What we found is that essentially this one over here would actually have quite a bit of torsional strain. Why? Because check it out, I have these hydrogens that are poking at each other. They're basically running into each other's space. So that would be one source of strain. Another source of strain would be that you have these hydrogens down here that are pretty much in each other's way. Okay? They're also eclipsed. Okay? So this would not be the best conformation for cyclohexane.

Now, over here on this one, this one is way better because we actually don't have any direct torsional strain. Now you might be wondering, well Johnny, I see that we have these hydrogens here that are facing the same way, but they have a carbon in between. That means they're actually pretty far apart from each other. Okay? There's actually very little torsional strain on this kind of conformation. Okay. And I wanted to tell you guys that it turns out that this is what cyclohexane is actually going to look like in real-life. In real life, instead of having 120 degree bond angles and having everything be eclipsed, all the hydrogens be eclipsed, instead what it does is it forms a puckered conformation and turns into what we call a chair.

And later on, when I talk about cyclohexane, and they have almost no torsional strain, and they have almost no torsional strain. So they are like the ideal cycloalkanes because they have pretty much the perfect bond angle, and because they are all twisted in that chair conformation, there's no torsional strain or very little torsional strain.