Learn about Organic Chemistry 3, in this comprehensive video by bannanaiscool.
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Rob Lederer: Okay, so what's this? Well, alright one, two, three, four, five isn't longest continuous change of carbons? No branches on there that I can see, and so therefore, that's going to be pent is five ane, single bond and that's pentane. Now, your teacher is going to try to be tricky, right? They going to do this or she is going to do this, you're going to put the carbon up there, and then you would say what's that? And you are going to say oh! There is a branch there, there is methyl on it. There is no methyl on there. Look. This is the longest continuous chain, five. Remember? So, the thing is this is going to still be pentane. Whether it's pent or not that's okay. The longest continuous chain is five. The next one is little different because it's got one, two, three, four, five carbons in it so it's an isomer of pentane. But longest continuous chain one, two, three, four going that way or going that way or going this way. Now, you are saying well, okay, I get this there is a methyl branch here, it's here. Right? And there is a longest continuous chain, but do I say that the methyl is on the third carbon in or the second carbon in on the chain. Use the lowest number as possible that's the IUPAC rule, International Union of Physicists and Applied Chemistry something like that. That means then when you are trying to tell where the branch is in the chain, you are going to say okay, lowest number of possible this is the branch here is the chain. I know it's a butane and the methyl group is on the second one in because remember you can take this molecule turn it around, right? And it would then be from left to right the second one in, but doesn't matter. So this is going to be a methyl branch that is on the butane, but it's on the second carbon on the butane so we call it 2-methyl butane. Well that's cool. It gets crazy. Now, what about this one right here? Okay. Longest continuous chain of carbons one, two, three, four, it could be one, two, three, and four will make any difference by the way. One, two, three, four won't make any difference. I think I did that won't make any difference by the way. Now, so the longest continuous chain here is four, so you know that it's butane. Right? But this has branches. What do I do? It's okay. Its two work branches. There is a methyl branch here that's a CH3 and a methyl branch here. Hey, that's an ethyl. No, no. Its two methyls, you know that's coming later with the ethyl. Now look. So you've got a methyl, methyl there and a methyl here. So, where are they? Well, they are on the second and the third carbon in. Now, you are going to say well, it's a second carbon in this way, the second carbon in this way. Yeah, but once you choose one way to do it, you got to stick with that. So, you got to go there is a methyl there and the methyl on the second and the third carbon in on the branch that's going to be a methyl on the two and a methyl on the three. So, you've got methyls. How many? Two. That's dimethyl. You have to say dimethyl for two methyls. Then, you've got to say where they are? One is on the two and the other is on the three separate numbers from letters with hyphens and numbers from each other with commas 2, 3 di-methyl butane. Perfect, right? You can see that in the name. If I didn't give you this and just gave you the name, its butane draw for carbons, and then put a methyl on the second or in the methyl on the third one; beautiful way to name these. Isn't it great? Now, what about this one down here? Now, how we are going to get that one done? We are going to find the longest -- let's see one, two, three, four, five, six made that way, it can't go this way look, one, two, three, four, five that's not the longest continuous chain, don't pick it. Six is the longest continuous chain, so that's going to be a hexane that's a hexane. Now, where are the branches? Well, this is a branch and this is a branch. That's a two carbon branch. So what's that going to be called? Two carbo