 Okay, so let's try this problem. It's a symmetry problem. It says pick out which of the following compounds That does not possess a plane of symmetry. So let's go ahead and draw all these compounds at a sense. Okay, so a it says Sys 1 2 dimethylcyclo-propane And if you want to there's the model kit so you can start building these things while I'm drawing Show ourselves definitely which ones possess a plane of symmetry and which ones don't. The next one is this 1,3-dide hydroxycyclo-pentane Okay, so cyclopentane, and then it says cis. So we're going to make them both up 1,3-dide hydroxycyclo-pentane. Then the next one is trans-1,4-dibromo-cyclohexane so the cyclohexane and trans-1,4-dibromo Okay, let's see D trans-1,3-dide trans-1,2-dide hydroxy Cyclohexane Lastly, E is trans-1,3-dibromo-cyclo-butane So finally had cyclopropane. Okay. That's all right. It was kind of hard. Okay, so let's see if we can determine which one of these has symmetry but just by looking at these pictures Okay, so can you determine and some of them might have symmetry? Definitely A and B. A and B definitely, right? So we can Write that right. So A is not the right answer, right? B Remember it's because both of these are pointing up that it allows it to be cut in half like that, okay? So what about C, do you see this point of symmetry there? Well, if a bromine was pointing up, it would have a plane of symmetry. Okay, so definitely that but let's go ahead and build See if we can build this really quick while we're on video. They're both bromines, right? Okay So one's supposed to be up And the other one's supposed to be down, right? Okay, and it's supposed to be 1,4 So we got it on the one and the four carbons, right? Okay, because 1, 2, 3, 4 like that and When we look at this, one of them's pointing towards us And one of them's pointing away from us, right? Okay, so is there a plane of symmetry? Not if we cut it like this, right? Because one's down, one's up and one's down But if we cut it in half like this, right? We cut it in half like this. We're cutting each of those atoms in half too, okay? So this side is the exact same as this side, okay? So you can actually cut these kinds of things even though this is the trans Just down that section there, okay, so let's cut that one. So does that make sense that one? Okay, and you see a similar thing with this one. Do we need to build it? No, we don't build that cycle of beauty So it doesn't matter what atom is on here? Uh-huh, so that's why they did this one, is because probably the, so let's cross out these two answers Probably the most missed one is this one, because you just looked at those names and you were like, oh Totally, fluorine and bromine, those are opposite. They can't be But couldn't you cut like this one? No, so let's let's let's build this one and we'll actually put OH groups on there So it can look what it looks like. Okay, so when we do this one, one, two Because they're trans, right? If they were cis, then you can, whoops Fall off. If they were cis, then you could just cut it in half Like this because this hydroxyl group would be up there, right? You could just cut it in half like that, but since this one's down and this one's up You can't cut it in half because this is a hydrogen. This is a hydroxyl group. Okay You can't do it anyway. This has no point of symmetry in between the two OHs you couldn't cut Oh look, this one's up. This is like me going like this and me going like this, right? So look, if I cut it in half, is this the mirror image of this? Oh, I see what you're saying. That's what that's all it is. Okay, so is this the mirror image of this? So you got to make sure you're understanding, okay So that's the one without a plane of symmetry. Okay, any questions on that? Okay