Carboxylic acid naming
Carboxylic acids are named following IUPAC nomenclature. In general, carboxylic acids are named based on the number of carbons in the longest continuous chain, including the carboxyl group (-COOH). The suffix of this carbon chain is then replaced, as carboxylic acids always end in "-oic acid." An example is CH2O2, in which the longest continuous carbon chain is a methane. The -ane suffix is replaced, giving us "methanoic acid.". Created by Sal Khan.
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- can we put (E)- instead of trans- ?5:13(3 votes)
- Yes, that would be an equivalent name. Actually the E-Z nomenclature for alkenes is preferred because it's less ambiguous than the cis-trans nomenclature.(2 votes)
- I have a doubt; I dont understand the concept of "trans" which Sal was talking about in about the 5th minute. He says the functional groups are on opposite sides but i can spot only one carboxylic functional group. Can you please help me out? I understood the rest of the video clearly.(2 votes)
- Trans just means that one group is on a wedge and the other group is on a dash. Trans means opposite from each other, as opposed to cis in which they would be on the same side of the molecule.(3 votes)
- @2:25, would you not have to assign a chirality for the third carbon on the 3 methyl hexanoic acid?(2 votes)
- You would, but it isn't super important when you're just learning naming.(2 votes)
- Is there a difference between the entgegen notation and that of trans?(1 vote)
- Yes. E/Z describe absolute stereochemistry whereas cis/trans only tells us relative stereochemistry. E/Z can be used without confusion when you have 3 or 4 different groups attached to the double bond carbons which is where cis/trans starts to break down.(3 votes)
- Why are there no carbons? What does trans mean and what is it used for?(1 vote)
- There are carbons, at the end of every line is a carbon atom. This type of structure was covered in an earlier video:
And trans refers to the orientation of atoms around the double bond, which also will have been covered in a previous video:
- If a hydrocarbon has both COOH and CHO groups, then is it necessary that Carbon atoms of both of them should be included in the parent Carbon chain(1 vote)
- Sometimes it will not be possible to include both in the main chain in which case the carboxylic acid takes precedence and the aldehyde group will be on a side chain.
For example 4-methyl-3-(2-oxoethyl)pentanoic acid:
Does that help?
Note also that hydrocarbons are organic molecules that only contain carbon and hydrogen, so a carboxylic acid is not a hydrocarbon.(2 votes)
- Don't we have to specify where the carboxylic acid group was attached ?(2 votes)
- in chain form, u don't require as it is a terminating group but may require in cyclic compounds.(1 vote)
- What is the name for this molecule CH3CH2COOCH2CH3?(1 vote)
- What's the structural formula of tartaric acid?(1 vote)
- Can carboxylic acid be called carbonyl compounds?(1 vote)
Let's systematically name some carboxylic acids, so let's add a molecule that looked like this. Clearly a carboxylic acid, we have a carboxyl group right over here. Now to name it systematically, we do it just the way we've named our simple alkenes. When we first learned how to name any organic molecule, you look for the longest carbon chain. And the longest carbon chain is one, two, three, four carbons, so our prefix will be but-, so it's butan. Instead of calling it butane, instead of writing this e here, we know this is a carboxylic acid, it has this carboxyl group, so we butanoic acid. And you might wonder, don't we have to specify where the carboxyl group is? And if you look at how carboxylic acids are arranged, you can tell that the carboxyl group is always going to be at one end of a carbon chain, so you don't have to specify. In fact, you always want to start numbering at wherever the carboxyl carbon is. So if you have to number these, this would be the one carbon, the two, the three, and the four. So you don't have to specify a number for the carboxyl group. Let's do another one. Let's say we had something that looked like this. Let me put another carbon on there, just like that, and let's say that there's a methyl group. Now clearly, a carboxylic acid, but to name it systematically we just want to find the longest carbon chain. So we have one, two, three, four, five, six carbons, so our prefix will be hex-, so it's hexan. It's clearly not just a hexane, it's a hexanoic acid, it has this carboxyl group right here. This is hexanoic acid. And we're not done, because we still have this methyl carbon right over here, and it is on the-- we always want to start numbering at this carbonyl carbon. One, two, three, four, five, six. It is at the number three carbon, so this is 3 methyl hexanoic acid. Let's do one more. Let's say we had a molecule that looked like this. That's one, two, three, four, five, six, seven carbons. Then we have our carboxyl group just like that, and let's say that we had a double bond right over there. What would we call this? Well, once again, look for the longest carbon chain. We have one, two, three, four, five, six, seven carbons, so the prefix is hept-, so it's heptan. And actually let me be careful, this isn't an alcane. This has a double bond right here. So it's hepten. If this was just an alkene, we would just called heptene, but we're not going to put this last e here, because this is the carboxylic acid. And to specify where that double bond is, we need to start numbering, and we start numbering at the carbonyl carbon. One, two, three, four, five, six, seven. So you could either name this 3 hepten, and I haven't finished it yet, I haven't put this final e over here. Or you could name it hept 3 ene, just like that. This is the more typical one that you would see, because it tells you we have a double bond, and it starts at the number three carbon, goes from the three to the four carbon. But this isn't just a regular alkene, this is a carboxylic acid. So instead of writing that final e, for an alkene, we write it as we have a carboxyl group right here, so this is 3 heptenoic acid. And we are done. Actually if you wanted to get really fancy on this one right over here, you could see that these two carbons that are on the double bond, so this carbon and this carbon, it's kind of a range like this. Let me draw it like this. They both have other hydrogens off there that we didn't draw, they're implicitly there. But if you wanted to rewrite or redraw this molecule, you could draw it like this. You have two carbons, just like this. This one has a hydrogen popping up like that; that one has a hydrogen popping down like that. And then this carbon over here has this big functional group over here. We'll call that R. And then this one over here-- I'll do it in green-- has this other functional group, has these three carbons. We can call that R prime. And if you look at it this way, the functional groups are on opposite sides of the double bond. They're away from each other. So if you wanted to, you could also call this trans 3 heptenoic acid. And this will specify that these guys are on opposite ends. But this is only if you're assuming that I drew it in the actual three dimensional configuration in some way. Anyway, hopefully you found that useful.