 OK, so we're looking at this double bonded structure. It's called an alkane. What we were saying is that when you have just one sigma bond or a single bond, you can rotate freely around that bond. So does everybody see me being able to rotate freely? I can hold either side of those and rotate, rotate, rotate. You guys see that? But once you get to a double bond or a triple bond, for that matter, free rotation becomes impossible. So do you guys see me trying to rotate the double bond? It's not happening. So effectively, what we have in this structure is these two big groups, these two methyl groups, they're called, fixed in their orientation relative to each other. We cannot turn this thing. In order to make this methyl group be up here, we would have to break this bond, break this bond, reform this bond, and reform this bond. So you guys see that? It's a different structure. So when I turn this, this is not a different structure than this. Is everybody OK with that? But when I break a bond and reform a bond, that is a different structure. So free rotation does not make a different structure. That's like me going like this. And you're saying, OK, that's a different person, which you know it's not. So free rotation does not make me a new heat. But if you ripped off my arm, ripped off my leg, put my leg on my arm and my shoulder and my arm on my whatever, then I would be a different person, different molecule. But anyways, we call these things alkene, these things with double bonds. When the big groups are opposite of each other, that's trans. Or e, you'll see. E is this weird German word that we won't get in. So you can either call it trans or opposite of each other. When they're on the same side as each other, we call this cis or c. So a way that people remember this is z is on the same side. So if you want to remember that, that one. It's the easy way to remember it. So let's go back to what we were talking about last time. In this double bond, how many sigma bonds are there? One. And how many pi bonds? One. Is this the same structure as this? Same molecule as this? Are these the same molecule? What did I just say five minutes ago? Why not? Because you can't, you have to break the bond and reform. So watch the video if you said they're the same structure. Any other questions on this? Or any questions besides my questions for you guys? OK.