Nomenclature of aldehydes and ketones
Rules for naming aldehydes and ketones. Created by Jay.
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- At5:49you named the molecule Cyclohexane Carbaldehyde but you did not explain why that particular compound is called a Carbaldehyde.(37 votes)
- A carbaldehyde is an aldehyde that is attached to another entity which is often a ring system.(14 votes)
- At4:25why does the carbon of the phenyl get numbered 1? Looking at the previous examples, I would have expected the 1st carbon to be the one double bonded to the oxygen as that is the aldehyde.(17 votes)
- At12:06, why does Sal name the molecule "hexane dione" instead of hexadione?(8 votes)
- It is a basic rule in ketone nomenclature.....
that when it is a straight chain compound or a cyclic compound , we drop off the 'e' from alkane and put 'one'...
so a hexane becomes a hexanone ....
however in presence of two ketone groups in a compound... (diones)
the 'e' in alkane is retained and we add 'dione or trione ' to the IUPAC name..
(it says simply that in a single ketone group the two vowels clash, so a vowel is dropped off i.e 'e' ... else it would be hexaneone.. (which doesnt sound appropriate) )
i hope im making sense :)
ps: its jay and not sal(19 votes)
- Someone asked this before too, but I want to ask again:
Why does the Cyclohexane Carbaldehyde have a "Carbo" in it? Why wouldn't it just be named Cyclohexane Aldehyde, or Cyclohexanal, or Cyclohexaldehyde or something similar?(8 votes)
- Aldehydes take "-al" and "-carbaldehyde" suffixes. You can call it cycloheaxanal or cyclohexane carbaldehyde. Both are correct. Here are some websites for references: http://chemicalland21.com/specialtychem/nh/cyclohexanal.htm https://www.bluffton.edu/~bergerd/classes/CEM221/Handouts/nomenclature-2.pdf(8 votes)
- why is it benzophenone and not phenylphenone ?(5 votes)
- A phenyl group refers to an aromatic ring that is directly attached to the chain/group in question (think aniline, which can also be named phenylamine, Ar-NH2), whereas a benzyl group refers to an aromatic ring bonded to another carbon, the latter of which is then attached to the chain/group in question. So a phenyl alcohol (or phenol) is Ar-OH, and a benzyl alcohol is Ar-CH2-OH (where Ar stands for an aromatic ring, and the bolded part is the phenyl/benzyl group proper).
So when you have two aromatic rings with a carbonyl in the middle, "benzo-" refers to one of the rings as well as the carbon atom attached to the oxygen. This carbon atom is attached directly to the other aromatic ring, hence "-phen-". Since it's a carbonyl with carbon substituents on either side, you end with "-one". Benzophenone.(2 votes)
- At8:03, should it be named 'methylethylketone' or 'ethylmethylketone'? Generally, the 'ethyl' group would take precedence going by the alphabet but does it hold true with ketones too?(2 votes)
- This is a problem with rules and convention. The rules say that it should be ethylmethylketone. Unfortunately, it is often called methylelthylketone. In the U.S. it is sold as a paint solvent with the name "MEK". When writing formally, such as in a textbook or research paper, it should always be written as ethylmethylketone.(5 votes)
- At 4.38 while numbering why double bond of phenyl is not given continuous numbers?(4 votes)
- At11:44, why is the carbon bonded to the oxygen numbered 1? Shouldn't it have to be 2 as the ketone has an R group on either side?(3 votes)
- For the molecule at3:30, how can you know for sure if it is a cis or trans compound, since no hydrogen atoms are drawn in the structure?(2 votes)
- Hydrogens are assumed at any position where nothing is shown.
We know that a carbon (without a formal charge) should be participating in four bonds. Since the carbons at each end of the double bond have three bonds shown and no charge, they must have a fourth bond to hydrogen that isn't being shown.
Furthermore, the bonds to other carbons are shown and so there is only one 'space' left for each of the hydrogens we know must be present. Those spaces are on opposite sides of the double bond and so the molecule must be trans.(1 vote)
- At2:25why the benzene is considered a substituent even though its consists of 6 carbons (the chain has only 3 carbons)?(2 votes)
Voiceover: Let's look at how to name aldehydes and ketones And let's start with an aldehyde and just to refresh your memory about how to recognize an aldehyde right there's a carbonyl present right. A carbon double bonded to an oxygen and there's an alkyl group on one side and a hydrogen on the other side. And so if we wanted to name this extremely simple molecule over here on the left, right we know there are total of four carbons and it's an alkane, so we call this "butane." So if we look at a four-carbon aldehyde right over here on the right so when you number an aldehyde you want to make your carbonyl carbon number one. So, one, two, three and four. So we have a four-carbon aldehyde. And what we're going to do is drop the E and add "-AL" for aldehyde. So this would be "Butanal," right. So a four-carbon aldehyde is "butanal" with an "-AL"ending like that. Let's go ahead and look at some more examples. So once again we're going to number to give our carbonyl carbon the lowest number possible. And the aldehyde is going to take priority over things like double-bonds and alkyl groups and halogens and so let's go ahead and look at this one on the top left here. And so we want to number to give our carbonyl carbon the lowest number possible so one, two, three, four and five. And so we have a five-carbon aldehyde right. Well a five-carbon alkane would be "pentane." So if our five-carbon aldehyde would be "pentanal". So let's go ahead and write "pentanal" here. So "pentanal." And then we also have a substituent right at carbon four, we have a bromine so we have to go ahead and put that in. So a "four-bromopentanal" would be the iupac name for this molecule. Let's do this one over here on the right. And so once again we're going to number giving our carbonyl carbon the lowest number possible so one, two, and three. So we have three-carbon aldehyde but this one has a double bond in it so a three-carbon aldehyde would be called a "propanal" but since we have a double bond present we're going to call it "propenal." Alright, so we have "propenal" here. So let's go ahead and write that. So, "propenal." And then the double bond starts at carbon two right here so we can write "two-propenal." We also have a phenyl group coming off of carbon three. So we can write "three-phenyl," so "three-phenyl" in here. And if you wanted to specify the stereochemistry of the double bonds, right you think about hydrogen being here and hydrogen being here. And so when you think about this double bond here, the hydrogens are on opposite sides so you can say that's their [trans] or you could use the easy system and your highest priority groups are on opposite sides here, so this would be E. So go ahead and write E. So "E three-phenyl two-propenal" is one way to name this molecule. It's kind of the old way of doing it. If you want to do it the newer way, you would write E, and then you still have a phenyl group here so "three-phenyl" and for the new way you would write "Prop" and put the two in here so "Prop-two-en" and then "-al". So once again the two specifies where the double-bond is and you still have your "-al" ending. And since this is the more modern way of doing it. So these are both iupac names for cinnamaldehyde. So this molecule here is actually cinnamaldehyde which is the molecule that gives cinnamon it's smell. So this a fantastic smell, and you can steam distill cinnamon bark and isolate this molecule which is a great undergraduate organic chemistry lab to do and so that's cinnamaldehyde. Alright so another great smelling aldehyde over here on the left, is "benzaldehyde." So here we have "benzaldehyde." Which is such a common name that it's been incorporated into iupac nomenclature and benzaldehyde smells like almonds. This is another fantastic smell so labs of benzaldehyde are a lot of fun too. So if you see benzaldehyde, you can use that in your iupac name. And so if we look at it over here on the right you can see that benzaldehyde can form the base for the name for this molecule. So let's go ahead and write that over here. So we have "benzaldehyde.". And then we're going to number to give this carbon on our ring, number one. Right so we have two choices we can go around the ring clockwise or counterclockwise. And we know we want to give the lowest number possible to our substituents and so that would be by going around clockwise. So let's do that, so two, three and then four. So we have two substituents, right. We have a methoxy substituent here at carbon three. We have a hydroxy substituent here at carbon four. And so we need to put those into alphabetical order so H comes before M and so we're going to start with the hydroxies, so let's, hopefully we'll have enough room here. So "four-hydroxy" and then we have a "three-methoxy "Benzaldehyde" is the iupac name for vanillin. So vanillin of course is where we get our vanilla flavor from. So a fantastic vanilla smell so these are white crystals which have an amazing vanilla scent to them. So also a lot of fun to do labs with. Alright so a lot of aldehydes have nice smells to them. Let's look at two more aldehydes. Alright so let's look at the one on the left here right. So it's not benzaldehyde, we don't have benzene ring here anymore, we have a cyclohexene, so this one is going to be called "cyclohexane carbaldehyde." So, "cyclohexane carbaldehyde" is the iupac name for this. So, "carbaldehyde." Alright, let's look at this molecule over here on the right so this is two aldehydes in the same molecule. Alright so let's look at this, so it'll be one, two, three, four and five total carbons. And so it's two aldehydes, so it's going to be "dial" and it's five carbons total so it's going to be "pentane", so we could write "pentane." We could write "pentanedial" here. And if you wanted to put where the numbers are, so it'll be one, five, so you can put that in there. So "one-five-pentanedial" for two aldehydes. Alright, let's look at ketone nomenclature next and so just to remind you of the general structure of ketones. So once again you have a carbonyl, a carbon double bonded to an oxygen. This time you have two alkyler groups right, so you have two alkyler groups here and they can be the same or they can be different right. So I can write "R prime" here and either one would still be a ketone. So once again we looked at butane earlier, so our four-carbon alkane, "butane." And what about if we had a four-carbon ketone? So this right here is a four-carbon ketone so it wouldn't be butane it's an O N E ending. It's an "-one", so it would be "butanone." So we're going to drop the E here and add O N E. So "butanone." That gives us the iupac name for this molecule. So there's an old way of naming ketones which is to think about the two alkyl groups, right. So let's go ahead and look at that. There's a methyl group on this side, so let's go ahead and write "methyl" right here. and then on this side there is an ethyl group. right, two carbons so "methylethyl". and then "ketone" gives you the structure for this molecule too, so "methylethylketone" is kind of the old way of doing it. And normally you would put the E before the M just thinking about the alphabet but for this one it doesn't really matter, everyone knows what "methylethylketone" is, also abbreviated "MEK." So naming the alkyl groups is an old way of naming ketones which you will sometimes still see. Alright so let's do another one here. Let's look at a longer ketone so we want to number to give the ketone, the carbonyl carbon lowest number possible and so we start from the left. Alright so one, two three, four, five and six. So we have a six-carbon ketone. So it's going to be "hexanone." So let's go ahead and write that. So this would be "hexanone". And we need to identify where the ketone is this time. So, it's on carbon three here, so for longer molecules it's important to specify where it is. So it would be three-hexanone is one the ways to name this molecule. Again this is kind of the old way of doing it. So the newer way would be to write for this one, "hexan-three-one". And if you wanted to use the alkyl way of naming this molecule, you could say this is an ethyl. So you're gonna write "ethyl" here, so "ethyl." and on this side a three-carbonyl alkyl group is "propyl." So "ethylpropylketone" is just another way to name it. So several names for the same molecule. Alright ketones take priority over things like double bonds and alkyl groups and halogens once again. So if you look at this molecule you want to number to give your ketone the lowest number possible and not your double bond so we're going to start from the left again so one, two, three, four, five and six. So we have a six-carbon ketone. So that would be "hexanone" but we have a double bond present so it's going to be "hexenone" So we have "hexenone" as thinking about our base name here. And once again two ways to think about naming it right, so I can do "hexenone", so "hexene" and then we have our ketone, carbon-two. So "hexene-two-one" so the two goes with the "-one", to tell you where the ketone is. And then the double bond starts at carbon-four right here so, "four hexene-two-one." If you want to specify the stereochemistry of the double bonds, so once again you have the hydrogens on opposite sides so that would be trans or E, right. So you could just write "E" here. So "E-four-hexene-two-one" is one way to name this. Again, kind of the old way of doing it. If you wanted to name it another way, You could write "E" and then you can write "hex," and then "four-ene", so once again the four is going with the "-ene" part telling you where the double bond is and then you have the "two-one" as well. So whichever way you prefer. Alright, so let's look at two more examples here, for nomenclature of ketones. So what if you have a ketone in a cyclic molecule here? So if I just, if I think about what I have, it would be "cyclohexane", but I have a ketone in my ring so it would be "cyclohexanone." So let's go ahead and write that. So, "cyclohexanone" indicating we have a ketone present and so we know the ketones take priority over alkyl groups so we're going to give this carbon a number one on our ring. And we're going to choose to around clockwise because that gives the lowest number to our alkyl group. So we go two and three. And so we have a methyl group at carbon three. So it'd be "three-methylcyclohexanone" as the iupac name. Alright, and then finally what happens if you have two ketones in the same molecule here? So we want to give the lowest number possible so we start numbering from the left side so one, two, three, four, five and six. So we have two ketones, so that's going to be a "dione." So one way to name it would be to say well it will be, "hexane" and then we have two ketones, right, so "dione". So "hexanedione," the ketones are at two and four the carbonyl carbons are at two and four. So "two-four-hexanedione" is one way to do it. And of course you can also do it the more modern way, you can just write "hexane" right, and then after hexane, so hexane [as I've] told you six carbons, so you could write "two-four-dione" Alright so that's it for nomenclature of aldehydes and ketones.