Carboxylic Acid Naming
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Carboxylic Acid Naming
- 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.