Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

4. Alkanes and Cycloalkanes

Naming Cycloalkanes

Ringed structures are easy to name, you just need to use a new prefix (aka –cyclo)!

Hint: Benzene and a cyclohexane are NOT the same thing. Remember, benzene has double bonds in it!

Understanding Cycloalkanes

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How to find the root name for cycloalkanes

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So now we're just gonna start layering stuff onto these al canes and making the names more complex. Let's talk about what happens when you have a ring to structure. So cyclo alcanzar the name given to any time they ever ring inside of your Al cane. And we're going to start off with the easy ones, which is just monos I click compounds. Okay, Monos I click just means one ring, okay? And these air easy. All we're gonna do is we're just going to tach cyclo to the beginning of the route chain. Okay, so all of a sudden, heck sane becomes cyclo hexane. Alright, Um, if it's a ring, the route is assigned to the portion of the out came with the greater number of carpets. Now, where this comes into play is that usually it's really obvious which one is bigger or which one is going to get the route name. But sometimes it's not as obvious, meaning that sometimes you have both a long chain and they ring on the same structure. Most of the time. It's just gonna be either a chain or it's gonna be a ring. But sometimes some structures combined both What do we do if we combine? Both. Okay, well, then we want to do is you want to give the part with the greater number of change the roots?

In general, we assign the root name to the portion of the alkane that has the greater number of carbons

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Determining Root Name

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So just go down to this example for a second if we're not gonna finish it. But I just want you guys to tell me which one would be the root here. I have a four carbon ring and I have a six carbon chain here. I have a six carbon ring and a four carbon chain. So an example. A. Which one? What would be the name of the route? Carbon. Well, the root carbon is chain is a chain. It's the sick carbons here because the largest portion. So the route in this case would just equal Heck scene. Does that make sense? Because it's just a six carbon chain?
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example

Determining Root Name

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Now I look at example, B example be also has a six carbon portion, but that's in the ring, and that's the greater portion. So in this case, the route is actually going to be cyclo hexane. Does that make sense? Because now my ring is the part that's getting the route name. Does that hope that makes sense?
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Numbering Monocyclic Cycloalkanes

If you only have one substituent on your ring, the numerical location is unnecessary! 

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Why it is okay to omit a single location for monocyclics

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then, lastly, if there's only one substitution on your ring, Okay, So let's say you have a ring and you have one thing coming off of it. Okay? The location of that thing can be omitted. Okay? How does that make sense? Well, because if you have a chain, let me give you a chain. An example. Chain. Okay. Obviously it's like the ugliest chain ever. I didn't even do the zigzags. But if you have a chain and you add one thing to it, that thing could be in a lot of different places. It could be there, or I could erase it and I could put there or I could erase it. Or And I could put it right at the end. Those air, all different possibilities of where that stick could be. Do you just see how I'm saying that? Like, the location is gonna matter. That is a different location than that. Okay, but if I have a ring and I put it here, that's the same thing as if I put it here. And that's the same thing as if I put it here. All of them are the same because the ring I could rotate as much as I want, whereas the chain, if I put it in the middle, it's stuck in the middle. It's never going to go to the end. Does that kind of makes sense? So for a chain, you always have to say the location always notes location, but for a ring, location could be omitted. Does that make sense now? This is Onley true. If I have one group, if I have more than one branch. So let's say I have two branches now. You need to say what the locations are. Why? Because that is gonna be a very much different structure than that. And that's gonna be a different structure than that. So then, once I have two things, it breaks that rule. But I was trying to say, If you only have one thing coming off of your ring many times, that location will be omitted. Does that make sense? Cool

Time to complete those names. Let's give it a try.

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example

Name the following alkane

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So here's the substitute, Wint. Here's a substitute, Wint. So why don't you tell me the first one? What would be the name of that substitution? And if location is important, tell me what location would be a swell. So first of all, what is for? I mean, what is this for carbon thing? It's a cyclo beauty. Do you guys agree with that cyclo butane? But is it the main chain? Is it on the Is it the main route? No, it's not. It's a substitute. Went so remember. There's always an ending that we give every substitue in. What is that substitue? It's always get a Y L ending. So what that means is that this is actually gonna be called cyclo beautiful. Okay, The reason it's Cycle Bugle is because it's not the root. It's a substitute. Does that make sense? Then what's the location? The location would just be that it's on the first carbon of this. So be one cycle beautiful, because on my six carbon chain, that's gonna be the side that I want toe have the lowest number. It would be dumb for me to put this side as the lowest number because Then it would take me six carbons to get to the cycle. Beautiful. So there we go. This name is gonna be one cyclo beautiful. Heck, sing Makes sense. Sorry. My handwriting got really messy there. I'll try to make it better.
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example

Name the following alkane

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So for this one, What type of substitue it do I have? Well, for this one, I actually just have a four carbon chain. Okay, so the name for that would be just beautiful. Okay, does that you don't have a location. Technically, if I want to give it a location, I could give it the location One, because obviously I'm going to start. I'm gonna start numbering the ring wherever the first substitution is because I can number the ring from wherever. But since there's only one substitution on here, I could also just drop the one. And I could just call this beautiful cyclo Hexi. And what that tells the reader, is that Hey, I have a ring on. I have one thing coming off of it. It doesn't matter where you write that futile group because they're all the same, no matter what. Cool! Awesome. So now we know how to name cyclo al canes
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Great job! Did you remember to include the location for the first example? Remember, that location is not optional!

Introduction to Bicyclics

Bicyclics are also forms of cycloalkanes, but since they are not monocyclic, they have completely different rules for naming! (See next topic)

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What is a bicyclic molecule?

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Now I just want to introduce by psy clicks, and I'm not going to rigorously teach you how to name them here. Okay. In fact, I'm not gonna teach you how to name them. Unless you're Professor specifically asks. Okay, Because by psy clicks or kind of like, if he some professors want you to know them, some professors don't. But I'm just gonna teach you, no matter what, you should know. The basics of what by cycling is okay and by psychics are composed of two distinct rings attached along one bond. All right, so this would be an example of a bys. I click. And it's made out of two cycle heck scenes and the actual name for a bys I click of to cycle Texans is called a decline. So Declan just equals cyclo Heck, scene Bice, I click. Okay, Some professors also take a special interest in Declan's on. I will also be monitoring your class to see if I have to teach a separate section on Declan's as well. Some professors don't really care. Okay. What's important is that I just want you to know that a vice I click by the way this dotted bond here is the same thing as a regular bond. I'm just pointing out that this is the bond that shared case that would be a bicyclist molecule. Okay, now abridged compound is a type of by sockets. I click, and it's actually composed of three compound rings attached by what we called to Bridge Head. I know this is getting a little weird. Bridgehead Adams. Okay, so here's an example. This one's called nor aborning, and it's a very common is actually one of the most common bridge structures. And you're asking me, Johnny, where the three rings? I do not see three rings. Well, there actually are. There's this main thing down here that's actually just a weird way to draw cyclo hexane. Okay, so that's just a six member drain. Then I've got a five member ID ring if I go along one side and then up like that. So that's 15 member dring, and then it turns out that I have another five member dring if I go up the other side and up that thing. Okay, This thing in the middle that I keep pointing to is called the bridge. Okay, so it's like I don't know. Think about that. You're walking over a bridge and you're going from one side of the molecule to the other. The atoms that attach all of those are called the bridge had atoms. So that's what I meant by two bridgeheads. So this is called a bridge compound. All right, so these are going to get We have different ways of naming by psy clicks thes have a certain way of naming. But like I said, I'm gonna That's gonna be a separate section that I teach you on Lee. If you're Professor requires that, you know that I just want you to be familiar with what a bridge is. Okay, awesome guys. So with that said, let's go ahead and move on to the next topic.
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