Understanding Alkanes and Their Nomenclature

Hello organic chemistry students. In this video we're going to cover the introduction of alkanes and their nomenclature. We're not going to get into their physical properties. That's present in the textbook and you're welcome to read that if you would like. It's not information truly that relevant in this lecture video right here, but it's still important information to read. So what is a basic alkane? An alkane is a compound where all the carbon-carbon bonds are single bonds. Now, that's the basic definition of a hydrocarbon alkane. That definition still also works for a functionalized alkane, meaning it could have a double bond in it, but maybe it's a carbon to oxygen, carbon to nitrogen, or nitrogen-nitrogen double bond. But as long as all the carbons are singly bonded, that is still an alkane. So an example of this is this molecule right here, as well as this compound here. Both of them are considered to be alkyl. because the carbon-carbon bond framework is the same. Now, the next thing I'd like to really just show for a moment is this structure here and this structure right here. And the question I'd like to ask is, are these two compounds the same or are they different? And the same with these two. Are they the same or different? And this is going to kind of lay the groundwork for a future video. And these are the same compounds. How one... Earth are they the same compound? It's because of free rotation around the sigma bonds in this molecule. So as that bond rotates, this carbon right here is going to rotate up, as we see, as the same thing with this carbon there. So if you have a singly bond carbon to carbon, or any atoms that are singly bond, you have rotation in that bond. And that allows us to have several different conformations of the structures. And what we're talking about here is Newman projections. And that's going to be another video that we're going to be learning later on. But I just wanted to go ahead and plant that seed right now. So that is the basic introduction into alkanes. I know, nice and easy. What I'm going to do right now is go ahead and name the alkane on the left-hand side. It is butane. The one on the right-hand side is called butan-al. So we have butane, and this should be an E right here, and butan-al. We're going to get through all this nomenclature in this class. This Al comes from the aldehyde functional group right here. The bute part right here in both of them is telling us how many carbons. And I'm sorry, I didn't draw butane on the right-hand side, so let me add two more carbons, another carbon in. So the bute is telling us how many carbons are in this molecule. The An right here is telling us that... all the carbon-carbon single bond or bonds are singly bound together. No carbon-carbon double bonds. We're going to get into butanol later on. That's in the aldehyde ketone section. Right now, we're going to focus on just standard alkanes and some functionalized alkanes and getting into naming them. Now, the process of naming is called nomenclature. And let's see if it's possible for me to write this word correctly. Once again, I am the world's worst speller. So nomenclature is a big fancy word for saying, let's name this molecule. That's all it is. We're going to call it BERT. We're going to call it ERNI. Just kidding. We have a systematic way of doing nomenclature. So step one is going to be count the carbons. Now that sounds pretty simple. So we have to put another clarifying statement on this. Count the carbons in the longest carbon chain. Now this longest part is going to change. We're going to see how that's going to kind of evolve over time, but for right now we're looking at the longest carbon chain. So I'm just going to go ahead and draw a random molecule over here on the side. There it is. All right, step two. What we're going to do is give the prefix name for this molecule. Now the prefix name for the molecule is going to equal the number of carbons in the longest carbon chain right up above. So if we happen to have so many carbons, what is the prefix that we use? And these are names that we're going to have to just learn. So if we have 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. They do go higher than this. We are just looking at the first 10. So the first one right here is meth, m-e-t-h. The second one is eth. Third one, is prop for three, butte for four, pent for five, hex for six, hept for seven, oct for eight, non for nine, and oct. Oops, not oct. I'm sorry. Just had a memory. Let's get rid of that right there. Duck. Alright, so that's if we have so many numbers of carbons that we have to give the prefix for this molecule. Great. If we have the prefix, what about the suffix of this molecule? So coming over here, the suffix, what we're going to do is look at the carbon-carbon bonds. So here, look at the carbon-carbon bonds. If all single bonds, like we're looking at right here in the alkane, so single bonds, we are going to use the ending of A-N-E. Wow, what section are we in right here again? The alkanes, A-N-E, and that's where it comes from. This nomenclature is relatively current right now, and that's how we're seeing this kind of common sense naming. Now the fourth one right here we're going to add in substituents. And we're going to get to that here in a little bit. But I just want to focus on some standard nomenclature right here at the beginning. So looking at this one in white right here. We have one, two, three, four, five, six. Six carbons for step one. Six comes down here for hex. Go ahead and do this in green. Hex. The carbon-carbon bonds, all of them are single. And we have A, N, E. This molecule is... hexane right there. Wonderful. Let's practice this some more. All right, let's go to the next page to practice this a little bit. Actually, no, we'll keep it here, shrink this down so we can actually keep this, and let's go ahead and look at this molecule right here. Notice I'm changing the structure a lot. I'm really trying to show that no matter how it's drawn, this nomenclature still works the same exact way. So we have a carbon. Let me go ahead and highlight the carbons, and I'll do this in a green. Here's a carbon here, here, 2, 3, 4, 5, 6, 7, 8. If we have 8 carbons in this molecule, what we are looking at is oct for the prefix, and all the carbon-carbon bonds are single bonds, so this is octane. Just that simple. Now, I'm saying just that simple, and I know some of you are like, oh, this doesn't seem that simple, but once you practice it enough, it will get easier and easier, and then you'll be like... Wow, it's really not that bad. It is just that simple. But you're only going to get there by practicing. So please practice nomenclature as much as you can. And our textbook and our online learning does have a lot of practice examples. Let's go ahead and look at another one. This one right here. Actually, we'll make it... There it is. So now if I was to highlight the carbons in this one again here's one, two, three, four, five, six, seven, eight. Uh oh that looks just like octane up above and that is it. Notice drawing the same exact molecule accidentally, but that is octane. So right now, we can name 10 organic molecules. That's it. We're about to expand that into the thousands by doing step four right here. We are going to add substituents. What is a substituent? A substituent are groups that are on the parent chain of a molecule. Let me say that again. Substituents are groups that are on the parent chain of a molecule. What's the parent chain? The longest carbon chain, that definition that we're working on right now, this step one right here. So I'm going to give a simple one, and we're going to go through it. There it is. So now, right off the bat, we don't just see one carbon chain. We can go 1, 2, 3, 4, 5, or 1, 2, 3, 4. This right here for 5 is the longest carbon chain. What I highly recommend that you do is you circle the highest or the longest carbon chain and name that first. There's 5 carbons in it, so that is going to be pence. They're all singly bonded. AIM. Now, there's this one carbon hanging out by itself. One carbon gets the... the prefix name of meth. Now we cannot call this methane because it's not the parent chain. It is a substituent. If it's a substituent, we're going to use this new ending called YL. This implies that it's the substituent hanging off the parent chain. So here we have a methyl group, methylpentane. But now, where is that methyl group in this chain? We have Carbon 1, 2, 3, 4, 5, or 1, 2, 3, 4, 5. Luckily here, no matter which way we count, it's the same, and we go 3-methylpentane. That's important. We're not numbering from left to right or right to left, absolutely. We're going to have to follow a systematic way of doing this. And let's go ahead and get into that with the next example on the next page. All right. Going back to that 5-carbon long molecule, I'm going to put a group right here. Now, no matter which way we number this molecule, we are going to get 5 carbons on the parent chain. So there it is right here. 1, 2, 3, 4, 5. So we're looking at pentane. There is a methyl group hanging on the outside, and that's the methyl group. Now here, I can call this 2-methylpentane, or I can call this, oops, not 5. Or I can call it, ah. 4-methylpentane. Where on earth do these numbers come from? The 2-methyl comes from if I number it this way. 1, 2, 3, 4, 5. And then the 4 comes from the blue nomenclature right here. In our nomenclature, we are always going to use the numbering sequence that gives the substituent the lowest possible number. And that's why the name of this molecule is 2-methylpentane. Let me say that one more time. We give the We use the numbering system that gives the substituents the lowest possible numbering. That's going to be key. Very important right here. Now, let's go ahead and make a longer molecule. And I'm going to go ahead and put a group right here. And another group right here. Let's go ahead and do the same thing. We have a grand total of 1, 2, 3, 4, 5, 6, 7, 8. Or 1, 2, 3, 4. five six, one two three four five six, or one two three four five six, ooh seven. But for us, eight is more than seven. So here's our parent chain. Here is octane. Now if we look at these two substituents, this one right here, there's two carbons connected together, so that's going to get an ethyl abbreviation. And then there's two down here again as well, so that's ethyl. We're not going to call this ethyl ethyl. octane. We're chemists. We like to abbreviate names. So we know that there's an ethyl group on this molecule, and we're going to use di in front. This di is telling us how many ethyls are in the molecule. So if you have di, that's two. Tri, that's three. Tetra is four. And it goes above that. But that's where we're going to stop right now. There's a lot more nomenclature here, but we're keeping it at the basics. But now, where are those ethyl groups? Uh oh, let's number this molecule. 1, 2, 3, 4, 5, 6, 7, 8. Or in blue, 1, 2, 3, 4, 5, 6, 7, and 8. Wow, look at that. 4, 5, 4, 5. In this case, the numbering sequence is identical. It doesn't matter which one we do. And that doesn't happen a lot, but it happened right here. So we have 4, 5. diethyl octane. We're now numbering or adding in substituents onto this chain. We're in the tens of thousands of molecules. Let's make it the hundreds of thousands of molecules. Oops, that looks horrible. Put a little gap in there. There's that, here's this, and that. Alright, let's name this molecule. If we go through, we're going to find out that this is our parent chain right here in red, and has a grand total of 1, 2, 3, 4, 5, 6, 7, and 8s. If you notice, I like writing octane a lot for whatever reason. So that's the parent chain. This happens to be an ethyl group up above, and this one's a methyl group down below. Uh-oh, what do we do? How do we name this? We're going to default back to elementary school and follow alphabetical order. So ethyl is before methyl. This is for the naming of this. It's ethyl methyl octane. Now let's number it. We have 1, 2, 3, 4, 5, 6, 7, 8. And 1, 2, 3, 4, 5, 6, 7, 8. So no matter what, we're using 4 and 5 both ways. Great, so does it matter if I call this 4-ethyl-5-methyl-octane or 5-ethyl-4-methyl-octane? It does. The numbering sequence is identical. No, now because the numbering sequence is identical, And we're putting the ethyl first because of alphabetical order. We're going to use that in the naming of this molecule. We're going to give the ethyl 4 and the methyl 5 because everything is equal. Let's go ahead and take that same molecule. I'm going to put the ethyl group here and the methyl group there, changing its orientation. So now, here's our longest carbon chain. We know that has 8 carbons. 1, 2, 3, 4, 5, 6, 7, 8, right there. We have octane. We know we have a methyl group and an ethyl group. So the ethyl goes before methyl because of alphabetical order. SO. Now, what about the numbering? When we look at this, we're going to go 1, 2, 3, 4, 5, 6. So we have 3 and 6. When we do it in blue, this is going to be 3, this is going to be 6. Uh-oh, I've given you another example problem where the numbering is the same. I didn't mean to do that. So really quickly, I'm going to go ahead and erase this and this 3 and that methyl. Okay, I can't erase the methyl group right now. Darn it. So we're just going to have to leave it just the way it is right now. So there's 3 and here is 6. So as we did before, 3 goes first for the ethyl. and then six. Now it's not exactly like the one up above because we know we have to give the ethyl the priority because it is in alphabetical order. Okay now let's move this and actually make it a little smaller and move it up and I'm going to purposely try to get this right where we can look at this a little bit better. All right here's my ethyl and here are the two methyls. Kind of making this a little different here. So now here's our longest carbon chain. When we look at this, we have a grand total of 1, 2, 3, 4, 5, 6, 7, 8, 9 carbons. 9 carbons, non, all singly bonded, ane right there. Now, this is a methyl group, and this is a methyl substituent right here, and here's our ethyl. So to name this, we're going to call this dimethyl, because the D comes first, ethyl, nonane. Or do we? What should we do here? What is the di actually representing in this molecule? It's representing the number of methyl groups, right? So this di is telling us how many of these methyl groups that starts with M. So if that's the case, we still need to write ethyl first because E comes before M in our nomenclature. So the numbering sequence that we're using here, this di and tri and tetra, does not count into the alphabetical ordering. Never use that whatsoever. So this top one is incorrect because the ethyl is supposed to be above the methyl or before it. So here the ethyl group is on carbon 3 and those methyl groups are 1, 2, 3, 4, 5, 6. And we go 6, 6. We have to indicate where both of these methyl groups are and that's why we need the 6, 6 right here. If there was 10,000 methyls on that carbon, which is impossible because we violate the octet rule pretty badly, you have to write 10,006s right there. So we have to use the same number of substituents that are on that carbon to implicitly state what is on that carbon. And that is how we name some of our substituents. All right. Now, we have some common names that we need to learn. Right now, we're learning our... IUPAC nomenclature which has been really powerful and great. But if we look at this carbon chain right here, here's five. If I put this chain on it right here, I'm going to put some more carbons on it right there. This is our parent chain and we have a propyl group hanging off of it. That's not a problem. The first carbon in the propyl group is bound to this carbon chain right here. Wonderful. Oops, I'm using a different color so I apologize about that. Actually, let me just go ahead and erase that really quickly. There it is. Go back to white, so it's the same. Now, if you look at this, here is our longest carbon chain still. What on earth is this group? There's still three carbons in it, and it's a YL, it's a substituent. But it's bound off the middle carbon of the propyl group. This is what we call an isopropyl group, which is different than a propyl group. It's depending upon... how it's connected to the parent chain. Very important there. Now there's some other ones that we're going to go over. So right now the squiggly line represents our parent chain. So if we have a carbon connected to four carbons that's a beautiful But it's off the second carbon, so we call this sec butyl. And that's a common name that we're going to have to learn. Another one that's a very important one in organic chemistry is if we have four carbons in it, once again. Here's one, two, three, four carbons. That's butyl. Now it's shaped like a T and we call it a tert-butyl group, also abbreviated T-butyl. And these are some common names that you'll need to learn for this class in organic chemistry as a whole. Alright, let's start adding in a little bit more functionality into these molecules. And we're going to add in the halides, the halogens. If you have a fluorine, we're going to be using fluoro for the abbreviation. Cl is going to be chloro, Br will be bromo, and I will be, you got it, iodo. So if we draw this four carbon long molecule, and I'm just going to go ahead and put a Cl here, and an iodine here, and a bromine here. I'm going for broke. I'm making this difficult. Let's find the longest carbon chain. Here it is right here. Longest carbon chain, we have butane. for that. We have a chlorine, we have a bromine, we have an iodine. So the bromo goes first for alphabetical order, followed by chloro, then iodo at the end. Now we have to number it. I'm going to call this 1, 2, 3, 4, numbering from left to right, and then 1, 2, 3, 4, numbering from right to left. Which one gives all of our substituents the lowest possible numbering? If we use the ones in red, we're using 2, 3, and 4. It's pretty high. The one in blue is 1, 2, and 3. But we're not looking at the alphabetical order because the numbering sequence is different. We want to give the substituents the lowest possible numbers. So we're going to give this 1-bromo, 3-chloro, and 2-iodo-putane. And that's how we name these larger molecules. Now if we had multiple halogens on this we can use our di-nomenclature just like we did previously. So let's just put this in and I'm going to put two chlorines on the same carbon. This is still a butane, four carbons long. It is a dichlorobutane because there's two chlorines in it and both of them are hanging off the second carbon. So we call this di-di, I'm sorry, 2,2-dichlorobutane. And now if we put more carbon chains in we can get bigger and badder molecules in these systems. The last area of nomenclature that we need to talk about is that of cycloalkanes. Now, cycloalkanes are just going to be alkanes that are in a cyclic form. Notice here, there's no start or ending point. Even though you can clearly see this is where I started in an alkane or cycloalkane, there is no start or ending point right there. So any one of those carbons could be carbon one. Any one could be two. We just follow it in order. So here the nomenclature is pretty much the same. We have six carbons in this ring system, so it is a hexane, but it's in a ring structure. And what do we put on it? Cycloin front. Just that simple. If we were to have three carbons like this, this is called cyclopropane. There it is. Can we put substituents on these? Absolutely, and the nomenclature is exactly the same as up above. And let's go ahead and look at the cyclohexane and do this. I'm going to go ahead and just put in a nice complicated problem right here. There's that and an ethyl group. So here, our cyclohexane is going to be our priority group. That ring system is priority. So here is cyclohexane. We have two chlorines. We have a methyl. We have an ethyl. Remember, we don't use the D and the dichloro for alphabetical order. just the chlorine. So now chlorine comes before ethane because C comes before E and then methyl comes after that. Now we do have a dichloro system going on. So dichloroethylmethylcyclohexane. But where's carbon one? This is where the cyclo compounds are different. We're saying chlorine is the first carbon right here. We have to give the lowest numbering of substituents. So I could call this carbon one. 2, 3, 4 in blue, or I could call it 1, 2, 3, 4 in green. But in yellow, if I go 1, 2, 3, 4, 5, 6, that seems kind of crazy. We're giving some high numbers. We have to give the numbering so as the lowest possible numbering in this system. So to do that, we're going to have a 1 ethyl, 2 methyl, 4. four dichloro molecules. We have four, four dichloro, one ethyl, two methyl, cyclohexane. These molecules are big and complicated. They're pushing the limits of what we can do. This is really on the high end. We're going to look at more simpler systems. One chlorine, a methyl, maybe two methyls on the ring, and systems like that. And as a whole, we have now covered what the basic alkanes are. in terms of their nomenclature and what the functional group means as a whole. As always, I recommend going back and watching the video again, making sure to take notes on it. If you have any questions, please feel free to email me, see me in office hours, or come to a discussion section. I'm happy to help you the best I can. I hope each of you are doing well and I look forward to talking to you soon.

Hello organic chemistry students. In this video we're going to cover the introduction of alkanes and their nomenclature. We're not going to get into their physical properties.

That's present in the textbook and you're welcome to read that if you would like. It's not information truly that relevant in this lecture video right here, but it's still important information to read. So what is a basic alkane?

An alkane is a compound where all the carbon-carbon bonds are single bonds. Now, that's the basic definition of a hydrocarbon alkane. That definition still also works for a functionalized alkane, meaning it could have a double bond in it, but maybe it's a carbon to oxygen, carbon to nitrogen, or nitrogen-nitrogen double bond.

But as long as all the carbons are singly bonded, that is still an alkane. So an example of this is this molecule right here, as well as this compound here. Both of them are considered to be alkyl.

because the carbon-carbon bond framework is the same. Now, the next thing I'd like to really just show for a moment is this structure here and this structure right here. And the question I'd like to ask is, are these two compounds the same or are they different? And the same with these two. Are they the same or different?

And this is going to kind of lay the groundwork for a future video. And these are the same compounds. How one... Earth are they the same compound?

It's because of free rotation around the sigma bonds in this molecule. So as that bond rotates, this carbon right here is going to rotate up, as we see, as the same thing with this carbon there. So if you have a singly bond carbon to carbon, or any atoms that are singly bond, you have rotation in that bond. And that allows us to have several different conformations of the structures.

And what we're talking about here is Newman projections. And that's going to be another video that we're going to be learning later on. But I just wanted to go ahead and plant that seed right now. So that is the basic introduction into alkanes. I know, nice and easy.

What I'm going to do right now is go ahead and name the alkane on the left-hand side. It is butane. The one on the right-hand side is called butan-al.

So we have butane, and this should be an E right here, and butan-al. We're going to get through all this nomenclature in this class. This Al comes from the aldehyde functional group right here.

The bute part right here in both of them is telling us how many carbons. And I'm sorry, I didn't draw butane on the right-hand side, so let me add two more carbons, another carbon in. So the bute is telling us how many carbons are in this molecule. The An right here is telling us that...

all the carbon-carbon single bond or bonds are singly bound together. No carbon-carbon double bonds. We're going to get into butanol later on. That's in the aldehyde ketone section. Right now, we're going to focus on just standard alkanes and some functionalized alkanes and getting into naming them.

Now, the process of naming is called nomenclature. And let's see if it's possible for me to write this word correctly. Once again, I am the world's worst speller. So nomenclature is a big fancy word for saying, let's name this molecule.

That's all it is. We're going to call it BERT. We're going to call it ERNI. Just kidding. We have a systematic way of doing nomenclature.

So step one is going to be count the carbons. Now that sounds pretty simple. So we have to put another clarifying statement on this. Count the carbons in the longest carbon chain. Now this longest part is going to change.

We're going to see how that's going to kind of evolve over time, but for right now we're looking at the longest carbon chain. So I'm just going to go ahead and draw a random molecule over here on the side. There it is.

All right, step two. What we're going to do is give the prefix name for this molecule. Now the prefix name for the molecule is going to equal the number of carbons in the longest carbon chain right up above.

So if we happen to have so many carbons, what is the prefix that we use? And these are names that we're going to have to just learn. So if we have 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. They do go higher than this.

We are just looking at the first 10. So the first one right here is meth, m-e-t-h. The second one is eth. Third one, is prop for three, butte for four, pent for five, hex for six, hept for seven, oct for eight, non for nine, and oct. Oops, not oct. I'm sorry.

Just had a memory. Let's get rid of that right there. Duck. Alright, so that's if we have so many numbers of carbons that we have to give the prefix for this molecule. Great.

If we have the prefix, what about the suffix of this molecule? So coming over here, the suffix, what we're going to do is look at the carbon-carbon bonds. So here, look at the carbon-carbon bonds.

If all single bonds, like we're looking at right here in the alkane, so single bonds, we are going to use the ending of A-N-E. Wow, what section are we in right here again? The alkanes, A-N-E, and that's where it comes from.

This nomenclature is relatively current right now, and that's how we're seeing this kind of common sense naming. Now the fourth one right here we're going to add in substituents. And we're going to get to that here in a little bit. But I just want to focus on some standard nomenclature right here at the beginning. So looking at this one in white right here.

We have one, two, three, four, five, six. Six carbons for step one. Six comes down here for hex. Go ahead and do this in green. Hex.

The carbon-carbon bonds, all of them are single. And we have A, N, E. This molecule is... hexane right there.

Wonderful. Let's practice this some more. All right, let's go to the next page to practice this a little bit.

Actually, no, we'll keep it here, shrink this down so we can actually keep this, and let's go ahead and look at this molecule right here. Notice I'm changing the structure a lot. I'm really trying to show that no matter how it's drawn, this nomenclature still works the same exact way.

So we have a carbon. Let me go ahead and highlight the carbons, and I'll do this in a green. Here's a carbon here, here, 2, 3, 4, 5, 6, 7, 8. If we have 8 carbons in this molecule, what we are looking at is oct for the prefix, and all the carbon-carbon bonds are single bonds, so this is octane.

Just that simple. Now, I'm saying just that simple, and I know some of you are like, oh, this doesn't seem that simple, but once you practice it enough, it will get easier and easier, and then you'll be like... Wow, it's really not that bad. It is just that simple.

But you're only going to get there by practicing. So please practice nomenclature as much as you can. And our textbook and our online learning does have a lot of practice examples.

Let's go ahead and look at another one. This one right here. Actually, we'll make it...

There it is. So now if I was to highlight the carbons in this one again here's one, two, three, four, five, six, seven, eight. Uh oh that looks just like octane up above and that is it. Notice drawing the same exact molecule accidentally, but that is octane. So right now, we can name 10 organic molecules.

That's it. We're about to expand that into the thousands by doing step four right here. We are going to add substituents.

What is a substituent? A substituent are groups that are on the parent chain of a molecule. Let me say that again.

Substituents are groups that are on the parent chain of a molecule. What's the parent chain? The longest carbon chain, that definition that we're working on right now, this step one right here.

So I'm going to give a simple one, and we're going to go through it. There it is. So now, right off the bat, we don't just see one carbon chain. We can go 1, 2, 3, 4, 5, or 1, 2, 3, 4. This right here for 5 is the longest carbon chain.

What I highly recommend that you do is you circle the highest or the longest carbon chain and name that first. There's 5 carbons in it, so that is going to be pence. They're all singly bonded.

AIM. Now, there's this one carbon hanging out by itself. One carbon gets the... the prefix name of meth.

Now we cannot call this methane because it's not the parent chain. It is a substituent. If it's a substituent, we're going to use this new ending called YL. This implies that it's the substituent hanging off the parent chain. So here we have a methyl group, methylpentane.

But now, where is that methyl group in this chain? We have Carbon 1, 2, 3, 4, 5, or 1, 2, 3, 4, 5. Luckily here, no matter which way we count, it's the same, and we go 3-methylpentane. That's important. We're not numbering from left to right or right to left, absolutely.

We're going to have to follow a systematic way of doing this. And let's go ahead and get into that with the next example on the next page. All right.

Going back to that 5-carbon long molecule, I'm going to put a group right here. Now, no matter which way we number this molecule, we are going to get 5 carbons on the parent chain. So there it is right here. 1, 2, 3, 4, 5. So we're looking at pentane.

There is a methyl group hanging on the outside, and that's the methyl group. Now here, I can call this 2-methylpentane, or I can call this, oops, not 5. Or I can call it, ah. 4-methylpentane. Where on earth do these numbers come from? The 2-methyl comes from if I number it this way.

1, 2, 3, 4, 5. And then the 4 comes from the blue nomenclature right here. In our nomenclature, we are always going to use the numbering sequence that gives the substituent the lowest possible number. And that's why the name of this molecule is 2-methylpentane. Let me say that one more time.

We give the We use the numbering system that gives the substituents the lowest possible numbering. That's going to be key. Very important right here.

Now, let's go ahead and make a longer molecule. And I'm going to go ahead and put a group right here. And another group right here.

Let's go ahead and do the same thing. We have a grand total of 1, 2, 3, 4, 5, 6, 7, 8. Or 1, 2, 3, 4. five six, one two three four five six, or one two three four five six, ooh seven. But for us, eight is more than seven.

So here's our parent chain. Here is octane. Now if we look at these two substituents, this one right here, there's two carbons connected together, so that's going to get an ethyl abbreviation. And then there's two down here again as well, so that's ethyl. We're not going to call this ethyl ethyl.

octane. We're chemists. We like to abbreviate names. So we know that there's an ethyl group on this molecule, and we're going to use di in front.

This di is telling us how many ethyls are in the molecule. So if you have di, that's two. Tri, that's three. Tetra is four. And it goes above that.

But that's where we're going to stop right now. There's a lot more nomenclature here, but we're keeping it at the basics. But now, where are those ethyl groups? Uh oh, let's number this molecule. 1, 2, 3, 4, 5, 6, 7, 8. Or in blue, 1, 2, 3, 4, 5, 6, 7, and 8. Wow, look at that.

4, 5, 4, 5. In this case, the numbering sequence is identical. It doesn't matter which one we do. And that doesn't happen a lot, but it happened right here. So we have 4, 5. diethyl octane.

We're now numbering or adding in substituents onto this chain. We're in the tens of thousands of molecules. Let's make it the hundreds of thousands of molecules. Oops, that looks horrible. Put a little gap in there.

There's that, here's this, and that. Alright, let's name this molecule. If we go through, we're going to find out that this is our parent chain right here in red, and has a grand total of 1, 2, 3, 4, 5, 6, 7, and 8s.

If you notice, I like writing octane a lot for whatever reason. So that's the parent chain. This happens to be an ethyl group up above, and this one's a methyl group down below. Uh-oh, what do we do? How do we name this?

We're going to default back to elementary school and follow alphabetical order. So ethyl is before methyl. This is for the naming of this.

It's ethyl methyl octane. Now let's number it. We have 1, 2, 3, 4, 5, 6, 7, 8. And 1, 2, 3, 4, 5, 6, 7, 8. So no matter what, we're using 4 and 5 both ways.

Great, so does it matter if I call this 4-ethyl-5-methyl-octane or 5-ethyl-4-methyl-octane? It does. The numbering sequence is identical. No, now because the numbering sequence is identical, And we're putting the ethyl first because of alphabetical order.

We're going to use that in the naming of this molecule. We're going to give the ethyl 4 and the methyl 5 because everything is equal. Let's go ahead and take that same molecule.

I'm going to put the ethyl group here and the methyl group there, changing its orientation. So now, here's our longest carbon chain. We know that has 8 carbons. 1, 2, 3, 4, 5, 6, 7, 8, right there. We have octane.

We know we have a methyl group and an ethyl group. So the ethyl goes before methyl because of alphabetical order. SO.

Now, what about the numbering? When we look at this, we're going to go 1, 2, 3, 4, 5, 6. So we have 3 and 6. When we do it in blue, this is going to be 3, this is going to be 6. Uh-oh, I've given you another example problem where the numbering is the same. I didn't mean to do that. So really quickly, I'm going to go ahead and erase this and this 3 and that methyl.

Okay, I can't erase the methyl group right now. Darn it. So we're just going to have to leave it just the way it is right now. So there's 3 and here is 6. So as we did before, 3 goes first for the ethyl. and then six.

Now it's not exactly like the one up above because we know we have to give the ethyl the priority because it is in alphabetical order. Okay now let's move this and actually make it a little smaller and move it up and I'm going to purposely try to get this right where we can look at this a little bit better. All right here's my ethyl and here are the two methyls.

Kind of making this a little different here. So now here's our longest carbon chain. When we look at this, we have a grand total of 1, 2, 3, 4, 5, 6, 7, 8, 9 carbons.

9 carbons, non, all singly bonded, ane right there. Now, this is a methyl group, and this is a methyl substituent right here, and here's our ethyl. So to name this, we're going to call this dimethyl, because the D comes first, ethyl, nonane.

Or do we? What should we do here? What is the di actually representing in this molecule?

It's representing the number of methyl groups, right? So this di is telling us how many of these methyl groups that starts with M. So if that's the case, we still need to write ethyl first because E comes before M in our nomenclature. So the numbering sequence that we're using here, this di and tri and tetra, does not count into the alphabetical ordering. Never use that whatsoever.

So this top one is incorrect because the ethyl is supposed to be above the methyl or before it. So here the ethyl group is on carbon 3 and those methyl groups are 1, 2, 3, 4, 5, 6. And we go 6, 6. We have to indicate where both of these methyl groups are and that's why we need the 6, 6 right here. If there was 10,000 methyls on that carbon, which is impossible because we violate the octet rule pretty badly, you have to write 10,006s right there. So we have to use the same number of substituents that are on that carbon to implicitly state what is on that carbon. And that is how we name some of our substituents.

All right. Now, we have some common names that we need to learn. Right now, we're learning our... IUPAC nomenclature which has been really powerful and great. But if we look at this carbon chain right here, here's five.

If I put this chain on it right here, I'm going to put some more carbons on it right there. This is our parent chain and we have a propyl group hanging off of it. That's not a problem. The first carbon in the propyl group is bound to this carbon chain right here.

Wonderful. Oops, I'm using a different color so I apologize about that. Actually, let me just go ahead and erase that really quickly.

There it is. Go back to white, so it's the same. Now, if you look at this, here is our longest carbon chain still.

What on earth is this group? There's still three carbons in it, and it's a YL, it's a substituent. But it's bound off the middle carbon of the propyl group. This is what we call an isopropyl group, which is different than a propyl group.

It's depending upon... how it's connected to the parent chain. Very important there.

Now there's some other ones that we're going to go over. So right now the squiggly line represents our parent chain. So if we have a carbon connected to four carbons that's a beautiful But it's off the second carbon, so we call this sec butyl. And that's a common name that we're going to have to learn. Another one that's a very important one in organic chemistry is if we have four carbons in it, once again.

Here's one, two, three, four carbons. That's butyl. Now it's shaped like a T and we call it a tert-butyl group, also abbreviated T-butyl. And these are some common names that you'll need to learn for this class in organic chemistry as a whole.

Alright, let's start adding in a little bit more functionality into these molecules. And we're going to add in the halides, the halogens. If you have a fluorine, we're going to be using fluoro for the abbreviation.

Cl is going to be chloro, Br will be bromo, and I will be, you got it, iodo. So if we draw this four carbon long molecule, and I'm just going to go ahead and put a Cl here, and an iodine here, and a bromine here. I'm going for broke. I'm making this difficult.

Let's find the longest carbon chain. Here it is right here. Longest carbon chain, we have butane.

for that. We have a chlorine, we have a bromine, we have an iodine. So the bromo goes first for alphabetical order, followed by chloro, then iodo at the end.

Now we have to number it. I'm going to call this 1, 2, 3, 4, numbering from left to right, and then 1, 2, 3, 4, numbering from right to left. Which one gives all of our substituents the lowest possible numbering? If we use the ones in red, we're using 2, 3, and 4. It's pretty high.

The one in blue is 1, 2, and 3. But we're not looking at the alphabetical order because the numbering sequence is different. We want to give the substituents the lowest possible numbers. So we're going to give this 1-bromo, 3-chloro, and 2-iodo-putane.

And that's how we name these larger molecules. Now if we had multiple halogens on this we can use our di-nomenclature just like we did previously. So let's just put this in and I'm going to put two chlorines on the same carbon.

This is still a butane, four carbons long. It is a dichlorobutane because there's two chlorines in it and both of them are hanging off the second carbon. So we call this di-di, I'm sorry, 2,2-dichlorobutane.

And now if we put more carbon chains in we can get bigger and badder molecules in these systems. The last area of nomenclature that we need to talk about is that of cycloalkanes. Now, cycloalkanes are just going to be alkanes that are in a cyclic form. Notice here, there's no start or ending point.

Even though you can clearly see this is where I started in an alkane or cycloalkane, there is no start or ending point right there. So any one of those carbons could be carbon one. Any one could be two. We just follow it in order. So here the nomenclature is pretty much the same.

We have six carbons in this ring system, so it is a hexane, but it's in a ring structure. And what do we put on it? Cycloin front.

Just that simple. If we were to have three carbons like this, this is called cyclopropane. There it is. Can we put substituents on these?

Absolutely, and the nomenclature is exactly the same as up above. And let's go ahead and look at the cyclohexane and do this. I'm going to go ahead and just put in a nice complicated problem right here.

There's that and an ethyl group. So here, our cyclohexane is going to be our priority group. That ring system is priority. So here is cyclohexane.

We have two chlorines. We have a methyl. We have an ethyl.

Remember, we don't use the D and the dichloro for alphabetical order. just the chlorine. So now chlorine comes before ethane because C comes before E and then methyl comes after that.

Now we do have a dichloro system going on. So dichloroethylmethylcyclohexane. But where's carbon one? This is where the cyclo compounds are different. We're saying chlorine is the first carbon right here.

We have to give the lowest numbering of substituents. So I could call this carbon one. 2, 3, 4 in blue, or I could call it 1, 2, 3, 4 in green.

But in yellow, if I go 1, 2, 3, 4, 5, 6, that seems kind of crazy. We're giving some high numbers. We have to give the numbering so as the lowest possible numbering in this system.

So to do that, we're going to have a 1 ethyl, 2 methyl, 4. four dichloro molecules. We have four, four dichloro, one ethyl, two methyl, cyclohexane. These molecules are big and complicated.

They're pushing the limits of what we can do. This is really on the high end. We're going to look at more simpler systems.

One chlorine, a methyl, maybe two methyls on the ring, and systems like that. And as a whole, we have now covered what the basic alkanes are. in terms of their nomenclature and what the functional group means as a whole. As always, I recommend going back and watching the video again, making sure to take notes on it.

If you have any questions, please feel free to email me, see me in office hours, or come to a discussion section. I'm happy to help you the best I can. I hope each of you are doing well and I look forward to talking to you soon.

Transcript for:Understanding Alkanes and Their Nomenclature

Transcript for:
Understanding Alkanes and Their Nomenclature