Ketone Naming Ketone Naming
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- In the last video, we learned a little bit about aldehydes.
- And we saw that they have the general structure where you
- have a carbonyl group bonded to some type of carbon chain,
- or I guess in the simplest form, this could just be a
- hydrogen over here, and then they definitely will have at
- least one hydrogen bonded to the carbon in the carbonyl
- group, so this was an aldehyde.
- Now, very closely related to an aldehyde is a type of
- molecule called a ketone.
- And let's draw a couple of ketones just to make things
- clear, and then we'll think about what the difference is
- between a ketone and an aldehyde.
- So this right here, CH3, CH3, carbon right over here.
- This right here is a ketone.
- And you say, hey, Sal, that looks very
- similar to an aldehyde.
- I have a carbonyl group in both.
- So this right here is a carbonyl group.
- This right here is a carbonyl group.
- Let me write this: carbonyl.
- We have a carbonyl group in both.
- We have a carbon chain over here.
- This could be a general carbon chain here.
- We have a methyl group.
- So how is this different?
- And I think you'll see.
- It's this part that I haven't highlighted yet.
- In an aldehyde, there's two ways to
- think about an aldehyde.
- You could either say that, look, the carbonyl group is at
- the end of a carbon chain.
- So the next thing over is going to be a hydrogen.
- Or you could say that in an aldehyde, you have at least
- one hydrogen bonded to the carbonyl carbon.
- And the way I remember that, so you have a hydrogen there,
- and in the ketone you don't.
- The carbonyl group is embedded in a carbon chain.
- It is bonded to-- at least it is bonded to a carbon on
- either side, so over here you have a carbon.
- And the way that I remember the difference, and this is
- really just a little bit of a mnemonic just to memorize it,
- is aldehyde has an "h" in it.
- There's an "h" right over there, and an aldehyde has a
- hydrogen bonded to this carbon.
- So now that we at least have a reasonable understanding of
- what a ketone is, let's name a few, just
- to familiarize ourselves.
- So this right here is the simplest possible ketone.
- And it's called acetone, or that's its common name.
- And actually, the word ketone comes from the German word for
- acetone, which was I think instead of a "c" there, they
- had a "k," so it's like aketone.
- And they said, oh, this is a ketone.
- So this is the common name.
- Another kind of traditional or common way of naming a ketone
- is to name each of these groups, and it's kind of
- similar to the way that we named ethers.
- But instead of writing the word ether at the end, we
- write the word ketone.
- So here we have a methyl group, and we have another
- methyl group, so we have two methyl groups right over here.
- So this would be dimethyl ketone.
- This right here is dimethyl ketone.
- And then if you wanted the systematic way of naming it,
- you just look at the longest carbon chain, which is one,
- two, three carbons, so it's prop.
- Propa-, and instead of calling it propane, we get rid of that
- "e" over there and we would call it propanone.
- That tells us that this right here is a ketone.
- And you have to know where this double bond is.
- And actually, for propanone, you don't have to specify it,
- because if you know it's a ketone, you know that it has
- to have a carbon on either side of the carbonyl group, so
- you actually don't even have to specify where the
- carbonyl group is.
- But if you wanted to, you could say, OK, that's going to
- be on the two carbon.
- No matter what direction you start counting from, it's
- going to be on the two carbon.
- But the two is kind of optional for propanone.
- Let's do a couple of other ones.
- So let's say we had a molecule that looks like this.
- So the traditional way of naming it, you'd say, OK, on
- this end of the ketone, I have one, two, three carbons.
- So on that end, I have three carbons.
- That is a propyl group.
- And on this other side of the ketone right over here, I have
- only one carbon.
- That is a methyl group.
- So then you would just name them.
- And you name then in order of increasing chain size,
- molecule size, or group size.
- So this one you'd write methyl first. Methyl, because it's
- only one carbon.
- So this is methyl propyl ketone.
- This is kind of the traditional or the common way,
- often kind of the most used way, of naming this molecule.
- But the systematic way of naming it, you look at the
- longest carbon chain and you say, OK, I have one, two,
- three, four, five carbons.
- So it's going to be pent-.
- And then you want to start numbering it so that the
- carbonyl carbon has the lowest possible number.
- So you want to start numbering on the right side: one, two,
- three, four and five.
- So this right here, so we said the prefix would be pent-.
- So it's penton, and instead of saying it's pentane, you say
- it's pentanone.
- And to specify where the carbonyl group is,
- you say it's 2.
- This is 2-pentanone.
- And you might also see it written like this:
- Either one of these right here would be acceptable.
- Let's do a slightly more complicated example.
- Let's say we had something that looked like this.
- So we have something, a molecule,
- that looks like this.
- And let me stick some chlorines over here.
- So what would this be?
- Well, our longest chain, once again, is this cyclohexane:
- one, two, three, four, five, six carbons.
- And I'll just name this systematically right here.
- And the more complicated things get, the more
- systematic people will want to name it.
- So if we have six carbons right here, and they're in a
- chain, so this is cyclohexane.
- You'd put the "e" there if this carbonyl
- group wasn't there.
- But since it is, we would call this cyclohexanone, So this
- right here tells us to name it cyclohexanone.
- And then in a ring like this, this would implicitly be the
- number one carbon.
- So if this is the number one carbon and we want to number
- in the direction so that the next groups have the lowest
- possible number, so we want to make this the two carbon.
- So this is 2,2-dichlorocyclohexanone.
- Now, there's two more.
- And I'll just show these to you because these tend to be
- referred to by their common names.
- So I just want to show them to you real fast. One is this
- molecule right here, where we have a methyl group
- on this side: CH3.
- And over here, we have a benzene ring.
- Now, that first super simple ketone that we saw, we called
- this acetone.
- And so the common name here is actually derived from acetone.
- Instead of calling it acetone, because it doesn't have just a
- methyl group here, this is called aceto-, and instead of
- acetone, it's acetophenone, because we have this phenyl
- group, that benzene ring right there.
- Acetophenone, which is a pretty common molecule, and
- you'll see it referred to this way.
- Now, the other one that you might see every now and then,
- and I just want to expose it to you, is a molecule that
- looks like this, that has two benzene rings on it.
- It looks like that.
- And this is benzophenone.
- These last two I just really wanted to expose you to their
- common names.
- But, in general, I think you have a decent idea at this
- point of how to name at least the simpler chains, either
- with the common names, for example, propyl, or methyl
- propyl ketone, or 2-pentanone.
- And these are the more typical or maybe the
- easier naming examples.
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