Naming organic molecules. The terms alkanes, alkenes, alkynes, hydrocarbon, all of those are terms that you need to become familiar with and I'm going to go through what they all mean. So a hydrocarbon is exactly what it sounds like. I'm going to just write that here. Hydro, whoops, not hydrogen, hydrocarbon.
And it's exactly what it sounds like. A hydrogen and carbon chain. So when you go to like name and write these hydrocarbons, there's different, I guess, like types you can come up with. So an alkane means that they have all single bonds. The A-N-E ending means all single bonds.
But you do this procedure, whether it's single bonds, double bonds, or triple bonds. So first thing you're going to do is identify your longest carbon chain. Second thing you're going to do...
is ask yourself, are there double or triple bonds? Because that's when you'll change the ending. And then you ask, are there groups on any of those interior carbons? We call those branches. So like, are there branches coming off of that longest chain?
And then we number the molecule given these branches or giving the double or triple bonds like the smallest number. The most important thing to remember is that carbons make four bonds. It always has to make four bonds.
So the hydrogens kind of just... We put as many on there as we need to make sure that every carbon is making four bonds. This is the formula for alkanes.
Like if I told you you had six carbons, you would say C6 and you would say H. And then using this formula up here, 2 times 6 is 12 plus 2 is 14. So that is an alkane. Now if it's an alkene or an alkyne, this formula changes.
But for an alkane, that formula works. Here's an example of alkanes. How we, remember the first thing was to identify the longest carbon chain? That's because we need to identify what the name is going to be.
So if you have the prefix meth, so that's what you see here. Meth, it's one carbon, and it looks like this. F is two carbons, and prop is three, butte is four, pent is five, hex is six.
Hep is 7, Oct is 8, Non is 9, and Dec is 10. So those are the 10 that you guys need to memorize, and it's just telling you how many carbons. So Meth is 1, Eth is 2, Prop is 3, Bute is 4, Pent is 5, Hex is 6, Hep is 7, Oct is 8, Non is 9, and Dec is 10. So I'm going to show you how to use those. Okay, so if I have a single, if they're all single bonds, notice in this first example, they're all single bonds between the carbons.
The hydrogens don't matter, but between the carbons, if I'm looking at the carbons, I have all single bonds. And I circled my longest chain there. So my longest chain has four carbons. So if I go back and look at four, that is bute.
So I'm going to name it bute. And then because they're all singly bonded, I end it with the ending ain. So butane is the name of that compound. Now on my next one, I look at my longest carbon chain, and I see that it's bute again, because it's four carbons again.
But this time there's a double bond in there, so I have to make the ending ene. And then one of my other rules was you have to number it. So you don't have to do that with butane, because there's no double, triple bonds, there's no branches, nothing like that. But on... This one, there is a double bond, so we have to say where that is.
So I'm going to number it so my double bond has the smallest number. So I'm going to number it this direction, 1, 2, 3, 4. That means that that double bond is on the first carbon. So I'm going to put 1 butene.
Sometimes you see it written as 1 butene. Either way is appropriate. I prefer like this top way, but you can write it this bottom way as well. The last one, I'm going to circle my longest carbon chain.
This time I only have two carbons. So I'm going to go back. I'm going to look at two. That's F. So E-T-H-S. And because I have a triple bond this time, it's Y-N-E.
So normally I would have to say, like, which carbon is it on? But there's only two carbons. So it's 1-2 or it's 1-2.
Regardless, it's on the first carbon, no matter which direction you start counting. So I don't need to write the number. because it's on the same carbon no matter which way you go.
So here are some more examples. So what happens if we add... Add a substituent.
That is the same as a branch. So what happens when we add a branch? So I'm still going to look for my longest carbon chain. So I'm just going to go with this one.
You could choose to go with this one. You could choose to go with this one. That's about it. This is technically a shorthand.
There is a carbon here, so technically I have four carbons total, but I can only draw a straight line between three of them. There's no way for me to go from like one carbon to this one to this one and then to this one. There's no bond there. You can't like retrace the bond. I can't go backwards.
So my longest chain, I'm going to go ahead and do this one just because it's already circled, which makes that this is a branch. So my longest carbon chain three carbons in it. So that means my name is going to be prop and then they're all singly bonded so it ends in ain.
So propane is my longest chain and then this group here I have one carbon. When there's nothing written it means one. So if I go back and look at my one carbon the prefix is meth and we always end branches with yl. So that's what you see up here.
We always end branches with yl. So methyl Propane is the name. You might see it as 2-methylpropane because this methane group is on the second carbon. However, it's on the second carbon no matter which way you number.
If I had started with the other carbon as my first one and gone 1, 2, 3, it's still on the second, which is why there's no number in the formal name. All right, doing another one. So again, I'm going to look for my longest carbon chain. I can go straight across.
That's five. Let's bend and see how many it is. So I could go one, two, three, four, five.
So that's still five that direction. I could go one, two, three, four. Wait, one, two, three, four, five.
Yeah, that's still five. So no matter which way I go, I get five. So I'm just going to go ahead and do this one here since that's like the carbons that are closest to me. And I'm going to number them. I'm going to go 1, 2, 3, 4, 5. Even if I went the other way and did my numbering like 1, 2, 3, 4, 5, it didn't change that 3. So it doesn't really matter which way I number on this one.
I have 5 carbons, which if we go back, you can see that the 5 is pent. And then because they're all singly bonded, I'm going to end it in A and E. And then this group here coming off has two carbons.
So if I go back and look at my two carbons, oops, went too far, that's F. And remember, we end our carbon substituents in YL. So ethyl, and then it's on the third carbon.
Okay. What if our substituent is not a branch? So what if, I mean, what if it's not a carbon-based branch, right?
So far we've done like ethyl, methyl, you could have propyl, butyl, pentyl. Your branches are probably not going to get that high. You're probably not going to have longer than like a, maybe a butyl branch. But what if it's not a hydrocarbon?
What if it is a halogen? So halogens are the last group in your periodic table. You'll see, well second to last, noble gases are the last, but halogens, this group 17, we're going to see how we name it with halogens on our carbons. So every time, again, every time you have a bend, you have a carbon. So there's actually three carbons in this first one.
So that's my carbon chain. Three carbons is probe. They're all single bonded. If it wasn't single bonded, there would be a second bond there. That's how you would know it was a double bond.
So that means they all end in ane. And then fluorine. Fluorine is my halogen. So I drop the I-N-E ending and I add the O.
So fluorine becomes fluoro. And I put it on the first carbon. One, two, three.
So first carbon, I have a fluoro and propane is my longest chain. So just doing another one, my longest chain right here is one, two, three, four carbons. Four is butane.
And they all have single bonding, so that's ane, so butane. And then I have a chlorine group, so I drop the I-N-E and I add an O, so chloro. And then it's on the second carbon, so the two.
So two chlorobutane is the name of that carbon. Compound. So what if I have multiple substituents?
So again, let's remember that there's carbons here at every one of those bends. So these are chlorine. The purples are chlorine, not carbon. So I'm going to circle my longest carbon chain and it's four carbons. I have one, two, three, four, four carbons.
So that's butane. So they're all single bonded. So that's butane, bute for four and then A for... Ane for single bonds.
And then I have two chloro groups. So before I just had the one chloro group. Now I have two of them because I have two chlorines.
So how do I say two in science? Di. So di-chloro. And then I have to say where they are.
So I have one of them that's attached to my second carbon. And then one of them that's attached to my third carbon. So I separate those with a comma.
So 2, 3-dichlorobutane. You can also have compounds that kind of make a circle. These two are really hard to make because there's so many electrons in here that they sort of like push apart. So these are very unstable.
But basically pentane, 5-carbons, and bigger hexane, those make cyclical compounds. Those ones specifically with the single bonds are not so important. This is a shorthand way to write them. You can write them like this where you're showing every single carbon. But these ones are more stable.
So these are the ones that like exist in real life. However, these ones are less useful. Our most useful type is called an aromatic compound, which I'll get to in a second. But the simplest... Cyclic alkane you can have is this one with three, but again, that's not stable, so it won't exist.
So then your next one is four, which again is not stable, so it won't exist. So pentane, the cyclopentane, is our most common one, or is our smallest one that we can make. And notice it's pentane because I have one, two, three, four, five carbons.
So five carbons is pentane, and then cyclo just means that they're all connected in A. Circle. In this case, it's specifically a pentagon, but basically they're all in a circle, so we call them cyclo and then their name. So cyclopentane because there's five. Here I have one, two, three, four, five, six.
So cyclohexane. If you see them like this written as the shorthand, again, you're just counting the points. So one, two, three, four, five, six means hexane, and because they're all in a circle, we say cyclohexane.
Cyclohexane is fairly common and we get sort of two shapes. We get this chair shape which is what most of the molecules make and then this boat shape which is what very few molecules make because all of these hydrogens are like too close together and because they're so close to each other they they're all negative so they push away which pushes it into this chair position. You might see that question later as Like how does cyclohexane mostly exist? It exists in this chair position.
So we call it a chair in a boat. The chair is the one that is more common. And I said this word earlier, aromatic.
Aromatic means that it's a cyclo compound, but with double bonds. So this is how we show a double bond in shorthand. And it just in those aromatic means that those double bonds move around. So see, you can see it here, here and here. And then on our next one, we see it here, here and here.
That's because those double bonds are moving around. They're constantly shifting places. That's why it's called aromatic, because they move. The double bonds are less reactive and usually shorter.
However, in a cyclic compound, that's not true. So double bonds are usually shorter and they're usually more reactive. But...
With aromatic compounds, that's not true. These double bonds tend to be unreactive. They tend to be the same length as the single bonds. That's because the electrons are more evenly spread out. Because they're in a circle in a straight compound like this, electrons have to move back and forth.
They have to pass each other. Whereas in a cyclical compound, they can keep going around without passing each other. That's what makes them more evenly distributed.
You can... easily add substituents onto this. So a fluorine or a chlorine, we would just put that fluoro or chloro prefix on the word benzene. So these are called benzene rings. Again, very common.
It's the only one I'll ask you about. I'm not going to ask you about like a five carbon with double bonds. I won't ask you that.
I'll only ask you about benzene specifically. Because benzene is so common, it's in so many skincare products, it's in so many drugs, like medicines, prescriptions, we see it a lot. So that's the only reason we're really talking about it, but you can add whatever you want to it, and we name that just by putting it in front.
So fluorobenzene, chlorobenzene, that sort of thing. So the last thing I want to talk about is I briefly want to go back to one of these pictures, this one. So I only focused on the carbons when I was talking about this picture, which is fine. You don't really name based on hydrogens. You only name based on carbons.
So if I were going to draw 3-ethylpentane, I would draw that by saying pent. That means there's five carbons. So 1, 2, 3, 4, 5. Um, ane.
means that they all have single bonds, so I don't have to change that. And then I have a prefix of ethyl, so I have a two-carbon chain on my third carbon. So I'm going to count in three carbons, one, two, three, and on my three-carbon chain, I'm going to put another two-carbon chain.
So here's my ethyl group, and here's my pentane chain. Now I have to go through and add hydrogens. So the hydrogens add there, like they add as many as you need in order to make every carbon have four bonds.
So looking at this carbon, it's only making one bond. That means I need three hydrogens. This carbon here is already making two bonds, so I need two hydrogens. This carbon here is already making three bonds, so I only need one hydrogen.
This carbon is making two, so I need two hydrogens. This carbon is making the one bond here, so I need three hydrogens. This carbon is making two bonds already, so I need one. two hydrogens and this carbon is making one bond. So I need three hydrogens.
Um, so that's how we know how many hydrogens to put on. We're just trying to make every carbon make, um, as make four bonds. They all have to make four bonds.
If I had a double bond, um, let's do, wait, where's the double bonds? Here we go. So if I had a double bond, um, Like I, like, let me, I guess let me just make one up. So if I had butene, let's say I had one butene. Oh, that's the one we did up there.
Okay, so I would say bute is four carbons. And then ene is a double bond. So where is the double bond?
On the first carbon. So on the first carbon, I'm going to put a double bond. So that's it. And now I've done the whole name.
Now I need to add hydrogens. So this carbon is making two bonds. So it needs two hydrogens.
This carbon is making three bonds, one, two, three, so I need one hydrogen. This carbon is making two bonds, so I need two hydrogens. This carbon is making one bond, so I need three hydrogens. So that's kind of the same thing that you see up here. You had the first carbon with two hydrogens, which is what you have here, again with that one double bond.
The second carbon here only had one hydrogen. because it was already making three bonds. The third carbon had two hydrogens, which were not drawn on there.
And then the fourth carbon had three hydrogens. So that's how we know how many hydrogens to put on. It's this rule that I said in the very beginning.
Carbon always makes four bonds. All right, so head on over to your notebook. Get started on the practice. Let me know if you have questions.