How to name benzene derivatives, with examples. Created by Jay.
Want to join the conversation?
- At9:08,why did the aldehyde group got preference?Could it not be benzoic acid.If not why?(13 votes)
- because in order of preference of functional groups ''aldehyde'' comes before the group -OH
for more information refer to link below
also it gives the lowest no possible for the compound.(14 votes)
- Can I use Ortho, Meta, and Para if I use Benzene instead of xylene in the name? So Ortho Benzene?(5 votes)
- No, you cannot. Using "xylene" designates that there are two methyl substituents, so it is necessary in the name. Ortho-benzene would tell you that there are two substituents that are ortho to each other, but not what substituents they are.(10 votes)
- what is meant by lowest sum rule(1 vote)
- The lowest sum rule states that, when you can number a chain from two different ends and get two different sets of numbers for the substituents, you choose the name in which the sum of numbers is the lowest. For example, you might name a compound as 3,9-dimethyldecane or 2,8-dimethyldecane. The second name has the lowest sum of numbers, so that is the correct name.
Similarly, you might name a compound 3,4,9-trimethyldecane or 2,7,8-trimethyldecane. The sum of the numbers in the first name (16) is less than the sum of the numbers in the second name (17). But the first name is incorrect because another rule takes precedence: the rule of first point of difference. Here, the name that has the lower number at the first point of difference is the correct one. Thus, 2,7,8 is chosen over 3,4,9 because 2 is lower than 3. Note that this rule also gives the correct name for disubstituted chains.
The lowest sum rule is thus a special case of the rule of first point of difference. It works only for disubstituted chains. The rule of first point of difference works for all levels of substitution. Thus, it is preferable to avoid using the lowest sum rule and use instead the rule of first point of difference.(9 votes)
- At9:39Jay says methoxy for ether. However at3:29he mentioned something called an anisole that was the same. So why do we not use anisole?(4 votes)
- HI SweetShruti
Because when we name the organic compounds we have to see that which compounds possess greater priority ... The functional group with the highest priority will be the one which gives its suffix to the name of the molecule.
For your Question,, in that compound Aldehyde group has greater priority than the Ether and yes ofcourse the hydroxyl. therefore we have to write the Suffix of Aldehyde rather than ether (Anisole).
Hope it Answered your question!(3 votes)
- can I write a phenol as a hydroxybenzne?(3 votes)
- You can write it, and people will understand what you mean, but it is wrong. The only correct name is phenol.(5 votes)
- at11:00he called it 2,4,6-Trinitro toulene, can we also call it sym-Trinitro toulene(2 votes)
- Yes, sym-trinitrotoluene is one of the names that has been used.
But you should avoid the name because it is not an official name.
2,4,6-Trinitrotoluene is an accepted name, but the IUPAC name is
- At9:55why is the -OH branching off carbon 4 named as a hydroxy instead of the "special" name phenol?(1 vote)
- The aldehyde group takes higher priority in the naming than the OH group, so the base name of the compound is benzaldehyde.
The OH and OCH₃ groups are then named as hydroxy and methoxy substituents.(4 votes)
- At10:03,instead of being 4-hydroxy-3-methoxy benzaldehyde can it be 3-methoxy-4-hydroxy benzaldehyde?(1 vote)
- The first one is correct, as it is ordered alphabetically - the numbering does not come into play when determining what order they are in the name.(4 votes)
- What is the position of benzene in the priority table? How do we know whether it is a parent or a substituent in a given compound?(2 votes)
- So when using the OMP system you don't need to signify the number when naming? So for 4 bromophenol, saying 4 parabromophenol or para-4-bromophenol would be incorrect?(1 vote)
- You're just doubling up by doing that.
Either p-bromo... (p for para) or 4-bromo...
The preferred IUPAC name (PIN) uses numbers not o/m/p though(3 votes)
Benzene was first discovered by the great Michael Faraday. And at that time, chemists could figure out the molecular formulas of compounds, but they didn't know the exact dot structures. And so chemists knew that benzene contained six carbons and six hydrogens, but they weren't sure exactly how those atoms were connected. And so there were several different proposals for structures for benzene. And the winning structure was proposed by August Kekule who said that benzene contains six carbons in a ring, and then you have alternating single and double bonds in that ring. And the story goes that Kekule came up with this dot structure when he had a dream and he saw some snakes bite each other's tails. And the snakes then whirled around in a circle. And that gave Kekule the idea for the ring. So this is one possible dot structure for benzene but I didn't have to draw my double bonds in this place. I could actually show a resonance structure for benzene. I could take these electrons, move them over here and push these electrons over here. And then these electrons would be over here. And so a resonance structure for benzene. I could have my pi electrons over here, over here, and over here. So either one of these Kekule structures is an acceptable dot structure for benzene. Now remember, in reality, since these are resonance structures, the actual molecule is more of a hybrid of these two molecules. And with that in mind, sometimes chemists will prefer to represent benzene with the six carbons in a ring and with a circle here in the center to represent the delocalization of those pi electrons. So maybe this is the lazy way to represent benzene. And this is called a Robinson circle after the great synthetic organic chemist, Sir Robert Robinson. And so sometimes the Robinson circle is a useful way to represent benzene. And sometimes a Kekule structure is over here on the left. And you would use a Kekule structure if you're trying to show the mechanism of reactions that benzene does. Let's look at how to name derivatives of benzene. So here we have benzene with a methyl group coming off of it. And so you could just call this molecule methyl benzene. So that's one possible name for it. But most people don't call it methyl benzene. It's called toluene. So it's such a common molecule in organic chemistry that toluene an acceptable IUPAC name. And in this example, we have an alkyl substituent that has only one carbon. This methyl group has only one carbon versus the six in the benzene ring. Well, what happened if your alkyl group had more carbons than your benzene ring, which is the situation over here on the right. So if we count up how many carbons we have, we have a total of seven carbons. And so in this case, we're actually going to mean this is an alkane and name the benzene ring as a substituent coming off of our alkane. So a seven carbon alkane would be called heptane. So I can go ahead and write heptane here. Then I have a benzene ring coming off of carbon 4. And when you're naming a benzene ring as a substituent, so it would be C6, H5 substituent coming off of my ring here, we call it a phenyl group. So I have a phenyl group coming off of carbon 4. So this would be 4-phenyl heptane as the IUPAC name for this molecule. Let's look at some other examples where we see benzene with one group on the ring. And these are all very famous monosubstituted benzenes. And because they are so famous, their common name is acceptable in IUPAC nomenclature. So a benzene ring with an OH group on it is called phenol. And we can use that when we are naming molecules. Benzaldehyde would be an aldehyde coming off of a benzene ring. And benzaldehyde is, of course, famous for having the smell of almonds. It's a really, really wonderful smell which is also why you'll hear some of these molecules referred to as aromatic compounds. Originally, it was because of the smell. And we're going to see in future videos what aromatic means in a chemistry sense. Over here, we have a benzoic acid, a carboxylic acid functional group coming off of our benzene ring here like that. And so, here I have seven of the most famous and most common monosubstituted benzene derivatives. And so these are molecules that most professors will have you memorize because you can use these names when you're trying to name more complicated benzene derivatives. So commit these to memory. Let's look at some disubstituted benzene derivatives. So this molecule over here on the left has two methyl groups coming off of the benzene ring. And so this first molecule has a methyl group coming off carbon 1, and coming off of carbon 2. So we could call this 1, 2 dimethylbenzene. That would be an acceptable IUPAC name. But whenever you have a benzene ring with two methyl groups on it, the common name for that is xylene. And so if we wanted to call this molecule xylene, technically, all three of these molecules will be xylenes. They're all benzene ring with two methyl groups coming off of it. And so we have to distinguish these xylenes from each other. And so when you have two groups that are right next to each other on a benzene ring, in this case my methyl groups, my methyl groups are right next to each other on my benzene ring, we say that that relationship is ortho. So I could call this molecule ortho xylene. And that would be another acceptable name. And sometimes you'll just see an O there. So you call it o-xylene. And that's fine too. We go over here to this molecule. This is also xylene. But we can see the methyl groups are in slightly different positions. Right now, we would have 1, 3 dimethylbenzene. So 1, 3 dimethylbenzene would be an acceptable name for this molecule. And when you have two groups that are a carbon away from each other, so this relationship is said to be meta in organic chemistry. So you could call this a meta, let me take off that m here as I am running out of room here. You can call this meta-xylene. So this is meta-xylene or just m-xylene. And then finally another xylene molecule. This time our two methyl groups would be at carbons 1 and 4. So you call this 1, 4 dimethylbenzene. Let me go ahead and write that in. 1, 4 dimethylbenzene would be one IUPAC name for it. But again, most people would name this as a xylene derivative. So it's a xylene derivative. This time my two groups are opposite each other. So they're opposite each other on the ring. And we call this relationship para in organic chemistry. So you could say it's para-xylene or also p-xylene. Let's look at some more examples of disubstituted benzene rings. And so here we go. We're actually going to use the monosubstituted derivatives that we talked about above. So if I look at this molecule over here on the left, I can see that this is the phenol portion of the molecule. So I can go ahead and say that this is phenol. And then in terms of identifying the bromine, I have two options here. I could use a number. I could say that bromine is at carbon 4. So I could call this 4-bromophenol. And that's an acceptable IUPAC name. Or I could use the OMP system that we talked about above. And when you have two groups that are opposite on the ring, we call that para. So I could also call this molecule para-bromophenol. And that's an acceptable name as well. Or I could even shorten it to p-bromophenol. Let's do this disubstituted benzene ring over here. And if I look at it, I can see that is benzoic acid. That's one of the ones that we memorized above. So I can go and write the parent name as being benzoic acid right here. And I now have to identify my substituent coming off of my benzene ring. So benzoic acid would make this carbon 1. And then my substituent is coming off of carbon 3, and my substituent is a nitro group. So I could call this 3-nitrobenzoic acid. Or I could say that the relationship between those two things coming off my benzene ring would be meta. So I could call this meta-nitrobenzoic acid. So let me see if I have room here. So meta-nitrobenzoic acid. Or I could just say m-nitrobenzoic acid. So all of those would be correct IUPAC names. Let's look at polysubstituted benzene derivatives now. And so these are actually two of the more famous examples that we could do. Once again, we're going to try to find a monosubstituted parent name here. And if I look, I can see that right here, this would be benzaldehyde. And so usually aldehydes have precedence over alcohols. And so that's why we're going to name this as a benzaldehyde derivative. So I'm going to go ahead and-- let's see, just to make sure I have enough room to start naming it by saying the parent name is benzaldehyde right here. And since the aldehyde gets precedence, this would get a carbon 1. We want to get the lowest number possible to our substituents coming off my ring. So I'm going to go this way. And I can see that I have a group coming off of carbon 3. And it's an ether group. So we talked about how to name ethers as substituents. This would be a methoxy substituent. So this would be coming off of carbon 3. So I'm going to write 3-methoxy benzaldehyde like that. And then I go over here to carbon 4. And I could say I have an OH group. And if I'm naming an alcohol as a substituent, I would call this a hydroxy or a hydroxyl group. And I'm going to say that this is a hydroxyl group at carbon 4. So 4-hydroxy-3-methoxy benzaldehyde would be the IUPAC name for this molecule. This molecule is better known as vanillin. So the smell of vanilla is probably my favorite smell. So I really enjoyed doing labs that involved the vanillin molecule. Let's do one more, another extremely famous example. I can see that I'm trying to find a monosubstituted benzene derivative, that would be toluene right here. So I'm going to go ahead and put toluene as my parent name. And that would make this carbon 1. The methyl group would become carbon 1. So I go ahead and number to get the lowest number possible. And I can see that I have three nitro substituents located at 2, 4, and 6. So to finish my IUPAC name, it would be 2, 4, 6. I have three nitro, so that would be tri- as my prefix, so trinitro toluene. And so this is also a very famous molecule. It's not normally called 2, 4, 6 trinitro toluene. Most people in the general public would, of course, know this as TNT. So the famous explosive. So this would be TNT. And we just named it. Of course, the name comes from the nomenclature for polysubstituted benzene derivatives. So hopefully this video just shows you an introduction as to how to name molecules with benzene in them.