Benzene Nomenclature Overview

Hello organic chemistry students. In this video we're going to be talking about benzene and the nomenclature behind it. Now benzene that we've already seen already has the molecular formula C6H6. Now there's so much more behind the story of how benzene was discovered and we're not going to get into that in these videos. We'll talk more about that in lecture. But in this video we're going to look at this this standard molecule that we have given the name benzene and we're going to talk about the nomenclature involving it. So if we were to take a benzene ring, and keep in mind it has a high degree of resonance in it so we can use this donut representation of it. If I was to put this isopropyl group on it, how would we call this as a name? The way that we name these molecules is that we would call this as our parent chain that I'm dotting out. In solid, this is our substituent. The substituent is isopropyl. It's not propyl because it's coming off the second carbon of these. propyl chain, so isopropyl, and it would be called isopropylbenzene. There's no need to indicate one isopropylbenzene because there's only one substituent on the ring, and that's the basic nomenclature of benzene with monosubstituents. We can also look at this if we have a benzene ring and put on a nitro group that we've seen before. This molecule, very cleverly, is called nitrobenzene. So as you're kind of seeing, the nomenclature of these molecules is pretty straightforward. Now, if we had a chlorine on it, what would we call it? That's right, before I can even draw it, you have it. This is called chlorobenzene. Now, there are several common names for some monosubstituted benzene systems, and we have to learn these names. We're going to talk about some in this video, some more might be discussed in lecture, but the key ones that we want to talk about right now is this one right here, where we have a methyl group on it. This one is called toluene. Now if we had to write out the molecular formula for toluene, one way of doing this as an abbreviation would be PHCH3 or PHNE. This right here represents a phenyl group and we'll talk about what that means here in a little bit. So toluene is one common name that we need to learn. Another one is if we had an OH on this aromatic ring. Oh, that's a horrible OH. This one is called phenol. Continuing on, if we have the six-membered ring and we put an NH2 on it, this is called aniline. And then if we put a carboxylic acid on it, this is called benzoic acid. And then there's other ones as well. But for this video, I'm going to stop right there. We will talk about other ones in lecture. And they're also fair game for quizzes and exams. These are just four of many common names for monosubstituted benzenes. When I was in school, I was responsible for memorizing almost 200 different monosubstituted benzenes when memorization was key. Luckily here, we're just going to stick to probably anywhere between four and ten monosubstituted benzenes. Here are some right there. Let's go ahead and talk about the disubstituted ones. So, disubstituted benzenes have an interesting pattern of nomenclature. Disubstituents. I'm pretty sure I'm misspelling substituent there, but we're just going to go with that. So, I'm going to use X and Y to indicate substituents. Here's X and Y right next to each other on the ring. Here's X and Y separated by one carbon. And when I say that, I mean the X on the carbon it's attached to and the Y on the carbon it's attached to is separated by one carbon. And here's X and Y on opposite sides of this six-membered ring. When they're directly next to one another, this is what we call the meta position. I'm sorry, not the meta position. I got ahead of myself there. Here's the eraser. That was quick. That's called the ortho position. When there's one carbon in between, that is meta. And then when they're on opposite sides of one another, that is called the para position. So if we have a disubstituted ring system, we have to use this ortho, meta, para nomenclature. So if we were to have this molecule right here, we have bromo, chloro, benzene. But which pattern does it follow up above? That's right, meta. So we put a lowercase m in front. You could write the name meta out if you want to, but lowercase m, we can use this ortho here, m, or para for the abbreviations, and that is perfectly acceptable. But notice. There's no numbering in disubstituted benzene systems. Now, what if we had this molecule right here? Here, you might be thinking, oh, it's a hydroxychlorose species. Nope. This right here is one of those common names that you have to memorize in this class, and that is phenol. There's also a chlorine on this phenol ring system in the para position. Para. chlorophenol. And that's disubstituted benzene rings. What about multiple substituents? So we're going to call this a polysubstituted benzene ring. So if we come back in here, and I'm going to put a chlorine down, a fluorine, and here's a bromine right here. We're going to default to the nomenclature that we know and love. We're going to name the parent chain first, benzene. We're now going to name everything in alphabetical order. We have bromo first, followed by chloro, followed by fluoro. We have to give this all the lowest possible numbering though. It's not based upon alphabetical order, so one, two, three, four. Now some of you might be thinking we should call this one, two, three, four because the bromine's first. Nope. We're going to use the white nomenclature because it gives the overall lowest possible numbering for this molecule. 4-bromo-1-chloro-2-fluorobenzene. If we happen to have a common name in here, we can use that common name as well. So here, let's put a toluene in. Here's a chlorine and here's a bromine. Our parent name is going to be toluene, which means, oops, let me go ahead and try to put an E in here to spell it correctly, which means that has to be carbon 1, 2, 3, and 4 because we're using the common name. We then have a bromine on this ring system on carbon 4, and then we have a chlorine on carbon 2. So 4-bromo-2-chloro-toluene is the name for this polysubstituted airing system. Same exact nomenclature that we've seen before. Let's go back to some other types of things. I'm going to draw this squiggly line for a parent chain, and say for some reason we have this aromatic ring on it, the benzene. This is when we use the name Phenyl. And that indicates that a benzene ring is a substituent on this parent chain. If we happen to have a CH2 and then the phenyl ring, this is what's called a benzyl group. Notice benzyl, not benzene. This is a benzyl because there is a CH2 group right there. Why would we ever use this? Why wouldn't we use benzene as the main parent chain? If the parent chain had a whole bunch of different functionality that we didn't want to try to name off of it. That's when we're going to use this. So here we're looking at carbon 1, 2, 3, 4, 5, 6, 7, and 8. We're looking at octadiene. We have double bonds at 1 and 7. And then we have this phenyl group on carbon 3. 3-phenyl-1,7-octadiene. Now... what if we really wanted to use the name benzene? We could do this. I highly recommend not doing this though. If we're doing this down below, and actually let me go ahead and just get rid of benzene in white, and I'm going to put this in blue right here. If we want to do this, we're saying this is the parent chain and this is our substituents. So in parentheses, we are going to have to write down something huge. We know on this benzene ring it's going to be carbon 1. We now have to indicate everything in this system. We have an octal or octadiene-al system. What is that implying? Eight carbons, a diene, and it's a substituent. We have to indicate in this that carbons 1 and 7 is where the double bond is located. Perfect. What about the phenyl group though? Oh my gosh. All of this is on carbon 3, and then we can put the 1 out here in front. If you notice, that's really darn confusing. It is. And it's really hard to do. That's why we like to use this nomenclature as shown up above, where we put the phenyl group in and just keep the nomenclature as simple as possible. When we're doing it this way, it's very easy and very common to make mistakes. The 1 indicates that this whole group is on the benzene ring. The three is indicating this is where the position is on the benzene ring, and this is the group on that three position of the octal on carbon one of benzene. Crazy, I know. So with that, that ends this video right here. But before I end the video, we need the code word for today. And the code word is our good friend phenyl, because it's going to save us so much time when we're doing nomenclature of these molecules. I hope this video gives you the basic concepts of nomenclature. We'll talk more about this in lecture. I hope each of you are doing well. I look forward to seeing you all in lecture. And I hope you're all having a wonderful day.

But in this video we're going to look at this this standard molecule that we have given the name benzene and we're going to talk about the nomenclature involving it. So if we were to take a benzene ring, and keep in mind it has a high degree of resonance in it so we can use this donut representation of it. If I was to put this isopropyl group on it, how would we call this as a name?

The way that we name these molecules is that we would call this as our parent chain that I'm dotting out. In solid, this is our substituent. The substituent is isopropyl.

It's not propyl because it's coming off the second carbon of these. propyl chain, so isopropyl, and it would be called isopropylbenzene. There's no need to indicate one isopropylbenzene because there's only one substituent on the ring, and that's the basic nomenclature of benzene with monosubstituents.

We can also look at this if we have a benzene ring and put on a nitro group that we've seen before. This molecule, very cleverly, is called nitrobenzene. So as you're kind of seeing, the nomenclature of these molecules is pretty straightforward. Now, if we had a chlorine on it, what would we call it? That's right, before I can even draw it, you have it.

This is called chlorobenzene. Now, there are several common names for some monosubstituted benzene systems, and we have to learn these names. We're going to talk about some in this video, some more might be discussed in lecture, but the key ones that we want to talk about right now is this one right here, where we have a methyl group on it.

This one is called toluene. Now if we had to write out the molecular formula for toluene, one way of doing this as an abbreviation would be PHCH3 or PHNE. This right here represents a phenyl group and we'll talk about what that means here in a little bit. So toluene is one common name that we need to learn.

Another one is if we had an OH on this aromatic ring. Oh, that's a horrible OH. This one is called phenol. Continuing on, if we have the six-membered ring and we put an NH2 on it, this is called aniline. And then if we put a carboxylic acid on it, this is called benzoic acid.

And then there's other ones as well. But for this video, I'm going to stop right there. We will talk about other ones in lecture. And they're also fair game for quizzes and exams.

These are just four of many common names for monosubstituted benzenes. When I was in school, I was responsible for memorizing almost 200 different monosubstituted benzenes when memorization was key. Luckily here, we're just going to stick to probably anywhere between four and ten monosubstituted benzenes. Here are some right there.

Let's go ahead and talk about the disubstituted ones. So, disubstituted benzenes have an interesting pattern of nomenclature. Disubstituents. I'm pretty sure I'm misspelling substituent there, but we're just going to go with that.

So, I'm going to use X and Y to indicate substituents. Here's X and Y right next to each other on the ring. Here's X and Y separated by one carbon. And when I say that, I mean the X on the carbon it's attached to and the Y on the carbon it's attached to is separated by one carbon. And here's X and Y on opposite sides of this six-membered ring.

When they're directly next to one another, this is what we call the meta position. I'm sorry, not the meta position. I got ahead of myself there. Here's the eraser. That was quick.

That's called the ortho position. When there's one carbon in between, that is meta. And then when they're on opposite sides of one another, that is called the para position.

So if we have a disubstituted ring system, we have to use this ortho, meta, para nomenclature. So if we were to have this molecule right here, we have bromo, chloro, benzene. But which pattern does it follow up above?

That's right, meta. So we put a lowercase m in front. You could write the name meta out if you want to, but lowercase m, we can use this ortho here, m, or para for the abbreviations, and that is perfectly acceptable. But notice. There's no numbering in disubstituted benzene systems.

Now, what if we had this molecule right here? Here, you might be thinking, oh, it's a hydroxychlorose species. Nope. This right here is one of those common names that you have to memorize in this class, and that is phenol.

There's also a chlorine on this phenol ring system in the para position. Para. chlorophenol. And that's disubstituted benzene rings. What about multiple substituents?

So we're going to call this a polysubstituted benzene ring. So if we come back in here, and I'm going to put a chlorine down, a fluorine, and here's a bromine right here. We're going to default to the nomenclature that we know and love. We're going to name the parent chain first, benzene.

We're now going to name everything in alphabetical order. We have bromo first, followed by chloro, followed by fluoro. We have to give this all the lowest possible numbering though.

It's not based upon alphabetical order, so one, two, three, four. Now some of you might be thinking we should call this one, two, three, four because the bromine's first. Nope.

We're going to use the white nomenclature because it gives the overall lowest possible numbering for this molecule. 4-bromo-1-chloro-2-fluorobenzene. If we happen to have a common name in here, we can use that common name as well.

So here, let's put a toluene in. Here's a chlorine and here's a bromine. Our parent name is going to be toluene, which means, oops, let me go ahead and try to put an E in here to spell it correctly, which means that has to be carbon 1, 2, 3, and 4 because we're using the common name.

We then have a bromine on this ring system on carbon 4, and then we have a chlorine on carbon 2. So 4-bromo-2-chloro-toluene is the name for this polysubstituted airing system. Same exact nomenclature that we've seen before. Let's go back to some other types of things. I'm going to draw this squiggly line for a parent chain, and say for some reason we have this aromatic ring on it, the benzene. This is when we use the name Phenyl.

And that indicates that a benzene ring is a substituent on this parent chain. If we happen to have a CH2 and then the phenyl ring, this is what's called a benzyl group. Notice benzyl, not benzene.

This is a benzyl because there is a CH2 group right there. Why would we ever use this? Why wouldn't we use benzene as the main parent chain? If the parent chain had a whole bunch of different functionality that we didn't want to try to name off of it. That's when we're going to use this.

So here we're looking at carbon 1, 2, 3, 4, 5, 6, 7, and 8. We're looking at octadiene. We have double bonds at 1 and 7. And then we have this phenyl group on carbon 3. 3-phenyl-1,7-octadiene. Now... what if we really wanted to use the name benzene? We could do this.

I highly recommend not doing this though. If we're doing this down below, and actually let me go ahead and just get rid of benzene in white, and I'm going to put this in blue right here. If we want to do this, we're saying this is the parent chain and this is our substituents.

So in parentheses, we are going to have to write down something huge. We know on this benzene ring it's going to be carbon 1. We now have to indicate everything in this system. We have an octal or octadiene-al system.

What is that implying? Eight carbons, a diene, and it's a substituent. We have to indicate in this that carbons 1 and 7 is where the double bond is located. Perfect.

What about the phenyl group though? Oh my gosh. All of this is on carbon 3, and then we can put the 1 out here in front. If you notice, that's really darn confusing.

It is. And it's really hard to do. That's why we like to use this nomenclature as shown up above, where we put the phenyl group in and just keep the nomenclature as simple as possible. When we're doing it this way, it's very easy and very common to make mistakes. The 1 indicates that this whole group is on the benzene ring.

The three is indicating this is where the position is on the benzene ring, and this is the group on that three position of the octal on carbon one of benzene. Crazy, I know. So with that, that ends this video right here. But before I end the video, we need the code word for today. And the code word is our good friend phenyl, because it's going to save us so much time when we're doing nomenclature of these molecules.

I hope this video gives you the basic concepts of nomenclature. We'll talk more about this in lecture. I hope each of you are doing well.

I look forward to seeing you all in lecture. And I hope you're all having a wonderful day.

Transcript for:Benzene Nomenclature Overview

Transcript for:
Benzene Nomenclature Overview