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- Everything we've named so far has been an alkane.
- We've seen all single bonds.
- Let's see if we can expand our repertoire a little bit and do
- some alkenes.
- So let's look at this first carbon chain right here.
- And actually, here I drew out all of the hydrogens just to
- remind you that everything we were doing before with just
- the lines, it really was representing
- something like this.
- When you start having the double bonds, and we'll
- explain it in more detail later on, it actually starts
- to matter a little bit more to draw the constituents, because
- there's actually different ways that you can arrange it.
- Because these double bonds, you can imagine, they're more
- rigid, you can't rotate around them as much.
- But don't think about that too much right now.
- Let's just try to name these things.
- So like we always do, let's try to find the longest chain
- of carbons.
- And there's only one chain of carbons here.
- There's one, two, three, four, five, six, seven carbons in
- that chain.
- So we're going to be dealing with hept,
- that is seven carbons.
- But it's not going to be a heptane.
- Heptane would mean that we have all single bonds.
- Here we have a double bond, so this is going to be an alkene.
- So this tells us right here that we're dealing with an
- alkene, not an alkane.
- If you have a double bond, it's an alkene.
- Triple bond, alkyne.
- We'll talk about that in future videos.
- This is hept, and we'll put an ene here, but we haven't
- specified where the double bond is and we haven't
- numbered our carbons.
- When you see an alkene like this, you start numbering
- closest to the double bond, just like as if it was a alkyl
- group, as if it was a side chain of carbons.
- So this side is closest to the double bond, so let's start
- numbering there.
- One, two, three, four, five, six, seven.
- The double bond is between two and three, and to specify its
- location, you start at the lowest of these numbers.
- So this double bond is at two.
- This is actually hept-2-ene.
- So this tells us that we have a seven carbon chain that has
- a double bond starting-- the ene tells us a double bond.
- Let me write that down.
- So this double bond right there, that's what
- the ene tells us.
- Double bond between two carbons, it's an alkene.
- The double bond starts-- if you start at this point-- the
- double bond starts at number two carbon, and then it will
- go to the number three carbon.
- Now you might be asking, well, what if I had more than one
- double bond here?
- So let me draw a quick example of that.
- Let's say I have something like, one, two, three, four,
- five, six, seven.
- So this is the same molecule again.
- One, two, three, four, five, six, seven.
- The way we drew it up here, it would look
- something like this.
- What if I had another double bond sitting right here?
- How would we specify this?
- Well, once again we have seven carbons.
- One, two, three, four, five, six, seven.
- So we're still going to have a hept here.
- It's still going to be an alkene, so
- we put our ene here.
- But we start numbering it, once again, closest to the
- closest double bond.
- So one, two, three, four, five, six, seven.
- But now we have a double bond starting at two to three, so
- it would be hept-2.
- And we also have another double bond starting from four
- and going to five, so hept-2,4-ene.
- That's what this molecule right there is.
- Sometimes, this is the-- I guess-- proper naming, but
- just so you're familiar with it if you ever see it.
- Sometimes someone would write hept-2-ene, they'll write that
- as 2-heptene, probably because it's easier to say 2-heptene.
- And from this, you would be able to draw this thing over
- here, so it's giving you the same amount of information.
- Similarly over here, they might say 2,4-heptene.
- But this is the specific, this is the correct
- way to write it.
- It let's you know the two and the four apply to the ene,
- which you know applies to double bonds.
- Let's do a couple more.
- So over here, I have a double bond, and I also have some
- side chains.
- Let's see if we can figure out how to deal with
- all of these things.
- So first of all, what is our longest chain of carbons?
- So we have one, two, three, four, five, six.
- Now we could go in either direction, it doesn't matter.
- Seven carbons or seven carbons.
- Let's start numbering closest to the double bond.
- The double bond actually will take precedence over any other
- groups that are attached to it.
- So let's take precedence-- well, over any other
- groups in this case.
- There will be other groups that will take precedence in
- the future.
- But the double bond takes precedence over this side
- chain, this methyl group.
- But it doesn't matter in this case, we'd want to start
- numbering at this end.
- It's one, two carbon, three carbon, four carbon, five
- carbon, six carbon, seven carbon.
- So we're dealing with a hept again.
- We have a double bond starting from the second carbon to the
- third carbon.
- So this thing right here, this double bond from the second
- carbon to the third carbon.
- So it's hept-2,3-ene-- sorry, not 2,3, 2-ene.
- You don't write both endpoints.
- If there was a three, then there would have been another
- double bond there.
- It's hept-2-ene.
- And then we have this methyl group here, which is also
- sitting on the second carbon.
- So this methyl group right there on the second carbon.
- So we would say 2-methyl-hept-2-ene.
- It's a hept-2-ene, that's all of this part over here, double
- bonds starting on the two if we're
- numbering from the right.
- And then the methyl group is also attached
- to that second carbon.
- Let's do one more of these.
- So we have a cycle here, and once again the root is going
- to be the largest chain or the largest ring here.
- Our main ring is the largest one, and we have one, two,
- three, four, five, six, carbon.
- So we are dealing with hex as our root for kind of the core
- of our structure.
- It's in a cycle, so it's going to be cyclohex.
- So let me write that.
- So it's going to be cyclohex.
- But it has a double bond in it.
- So it's cyclohex ene, cyclohexene.
- Let me do this in a different color.
- So we have this double bond here, and that's why we know
- it is an ene.
- Now you're probably saying, Hey Sal, how come we didn't
- have to number where the ene is?
- So if you only have one double bond in a ring, it's assumed
- that one end point of the double bond is your 1-carbon.
- When you write just cyclohexene, you know-- so
- cyclohexene would look just like this.
- Just like that.
- You don't have to specify where it is.
- It's just, one of these are going to be the double bond.
- Now when you have other constituents on it, by
- definition or I guess the proper naming mechanism, is
- one of the endpoints of the double bond will be the
- 1-carbon, and if any of those endpoints have something else
- on it, that will definitely be the 1-carbon.
- So these both are kind of the candidates for the 1-carbon,
- but this point right here also has this methyl group.
- We will start numbering there, one, and then you want to
- number in the direction of the other side of the double bond.
- One, two, three, four, five, six.
- So we have three methyl groups, one on one.
- So these are the-- let me circle the methyl groups.
- That's a methyl group right there.
- That's a methyl group right there.
- That's just one carbon.
- So we have three methyl groups, so this is going to
- be-- it's at the one, the four, and the six.
- So it is 1, 4, 6.
- We have three methyl groups, so it's trimethyl cyclohexene.
- 1, 4, 6-trimethylcyclohexene.
- That's what that is, hopefully you found that useful.