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Studying for a test? Prepare with these 5 lessons on Alkanes, cycloalkanes, and functional groups.
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Video transcript
Let's see if we can name this guy right over here. And so like always we always want to look for the longest carbon chain or the longest carbon cycle, and I think it's pretty obvious from this picture that we have a very long carbon cycle here, that we can start, or we can just look at this. We have one, two, three, four, five, six, seven, eight carbons in a cycle right over here. And so we can call this backbone, which is the backbone of our molecule right over here, this is cyclo octane. It's an octane in a cycle. It's an alkane because it's all single bonds right over here. So that is cyclo octane. Now let's think about the different groups that are attached to this backbone right over here. So first we can look at this one right over here, and we can ask ourselves, well, how many carbons are there? Well, there's one, two, three, four carbons that are attached to the backbones. So our prefix for when we're dealing with four carbons is bute, and it is in a cycle. So this is a cyclobutyl group. And we also have another cyclobutyl right over here. So this is another cyclobutyl group. Now let's think about this one right over here. How many carbons are there? We have one, two, three carbons. So our prefix when we're dealing with three carbons is prop, and they're in a cycle as well, so this is a cyclopropyl group. And now we can jump over to do these two groups right over here. We see that these are clearly the same groups. Let's count the number of carbons they have. They have one, two, three, four carbons. So if we're dealing with four carbons we would think about the prefix bute, but this isn't in a cycle and it's not in just a straight chain, it has this "Y" shape. And so the common name, when we end up with this "Y" shape, when we're attached down here, we're attached to one carbon here, and that's attached to kind of this carbon right over here, this is then attached to these other two, this is an isobutyl group, which we've seen multiple times before. And of course this one is an isobutyl group as well. So these are both isobutyl groups. Now the next thing we need to think about is how we can number it. We want to go back to our main carbon chain, which in this case is a cycle, and think about how we want to number. And the convention is to start numbering at the thing that is first in alphabetical order. And when we consider alphabetical order we think even the "C" in cyclo and we think of the "I" in isobutyl. If this was tert or sec you wouldn't think about the "T" or the "S" in secbutyl or tertbutyl, but for isobutyl you do consider the "I", for the cyclo's you consider the "C." And so when you look at it that way, all of the "C"s come before the "I"s, and then amongst the "C"s these all have cyclo's, but the cyclobutyl comes before cyclopropyl or cyclo octane. "B" comes before "P" or "O." So the thing that is first alphabetically are both of these cyclobutyls. So we can start numbering at where either of them attach to the main carbon backbone. I guess we should say those are both options, but we want to number from the one that is going to give us the total lowest numbering. So let's think about that a little bit. So we could say, let's number from here, let's make this the one carbon, and so that we hit something else as soon as possible, because remember we're trying to minimize the numbers here. We might want to go clockwise so we hit two right over here, three, four, five, six, seven. So in this situation where do we hit interesting things? We hit interesting things at the one, at the two, or where do we have groups attached to the chain? One, two, four, six, and seven. So that's one option. We'll have groups attached at one, two, four, six, and seven if we start right over there, and if we were to go clockwise. Our other option, is to start, and let me erase those, at this other cyclobutyl group here on the left. Let me erase these so I don't mess up the diagram too much. The other option is to start here, make this the one, number this as one, and then we would also go clockwise to hit the cyclopropyl, to hit something else as soon as possible. So two, three, four, five, six, seven. So now where we are getting interesting things? We have groups at the one carbon, the two carbon, the four carbon, the five carbon, and at the seven carbon. So actually this second numbering is preferable. Both of them have something at the one, the two, the four, and the seven, but the second one has something at a five while the first one had something at a six. So we would actually want to do this numbering right over here, and this is the numbering that we have now listed right over here. Let's now write what the name of this molecule actually is. So once again, we start first in alphabetical order. So we're going to start with the cyclobutyl groups. And we have two of them, one at the one carbon, and one at the four carbon. So we could say 1 comma 4. And since there are two cyclobutyl groups we would say dicyclobutyl. 1, 4 dicyclobutyl. And then what comes next in alphabetical order is the cyclopropyl. That comes before isobutyl. "C" comes before "I." That's at the two carbon. So then we can say 2 cyclopropyl. And now we can get to the two isobutyls. So there's an isobutyl at the five carbon and at the seven carbon. So we can say 5, 7, and since there's two of them we'd say di isobutyl. 5, 7 di isobutyl. And then we just give the name of the backbone. We've done the butyls, the dicyclobutyl right there, the cyclopropyl, the two isobutyls, and now we just write cyclo octane. And we are done. We have successfully named the molecule. And this kind of fun. It's like a secret code or something. You wouldn't expect naming organic molecules to be, I think quite so satisfying, but it is.