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- So far we've dealt with simple chains and rings of carbons.
- But let's think about what happens when things get a
- little bit more complex.
- Let me just draw a molecule here and we can think about
- how we'll name it.
- So let me draw it like that.
- So here we don't have a simple chain.
- It branches off at some point.
- So what we do in this situation is we find the
- longest chain in this molecule, and let's think
- about what the longest chain is.
- If we start here we get one, two, three, four, five, six,
- seven, eight carbons.
- If we start here we get one, two, three, four, five, six,
- seven, eight, nine carbons.
- So what we do is we look at the longest chain.
- The longest chain is this one right here.
- Let me do this in a different color.
- So this is one, two, three, one, two, three, four, five,
- six, seven, eight, nine carbons.
- And so this will be-- that will be kind of the core of
- our naming.
- So it's nine carbons.
- So that right here, longest chain, has nine carbons.
- You can kind of view this is the backbone of our molecule
- and also the backbone of our naming.
- Nine carbons, so we're dealing with a nonane.
- Remember, nine, non- for nine, and then -ane, because we're
- dealing with an alkane.
- We have all single bonds over here.
- Now, what do we do with this thing over here?
- Well, what's kind of sticking off of this chain?
- Well, we essentially have one carbon here that's attached to
- the chain, right?
- This carbon is bonded to a carbon on the chain.
- If we wanted to draw the entire molecule, we could draw
- carbon here and it would it be bonded to three hydrogens, but
- that is all implicit.
- But what is this thing right here?
- Well, it's one carbon.
- You might be tempted to say it's methane, but it's not
- methane because it's attached to other things.
- But it would be right to use the prefix meth-.
- So this right here, you would use the prefix meth-, so this
- is one carbon, so you would want to use the prefix meth-,
- but because it isn't the main chain, it is added to
- something else, we don't write methane, we write methyl.
- So let me write this right here: methyl.
- So this means it branches off longer chain.
- So this molecule right here would be called-- and
- actually, there's one more thing that we
- have to think about.
- This thing could have been-- we could just call it
- methylnonane.
- Let me just write that down right now.
- So we could just call this right from the get-go, we
- could call it methylnonane.
- But there's one problem with just calling it methylnonane.
- This is methylnonane, but so what's-- let me draw it.
- So the thing I just drew here, this is, one, two, three,
- four, one, two, three, four, five, six, seven, eight, nine.
- So that's the nonane.
- And the one I drew here's one, two, three, the methyl is
- right over here.
- That's what I just drew.
- That is-- let me do it in the same color.
- So this is what I just drew.
- But maybe, what if it was something like this?
- What if it was one, two, three, four, five, six, seven,
- eight, nine?
- And let's say that the methyl group was, instead of being
- right here, let's say the methyl group was right here.
- So how would you name these two things differently?
- This name right now does not differentiate between the
- methyl group being on this carbon versus the methyl group
- being on this carbon over here or this carbon over there.
- And what you do in this case is you number the carbons on
- the longest chain, on the main backbone, and you number them
- so that the methyl group is attached to the lowest
- possible number.
- So there's two possible ways to number this chain.
- You could start here as one, two, three,
- four, five, six, seven.
- Then you would say that this would be that the methyl group
- is attached to the seven carbon.
- Or you could start numbering from this end of the chain.
- It would be one, two, three.
- Or so it could also be attached to the third.
- Three, four, five, six, seven, eight, nine.
- So you want to number it so you're closest
- to the methyl group.
- So you want to start here.
- One, two, three, four, five, six, seven, eight, nine.
- So in this case, this would not just be methylnonane.
- This thing right here would be three.
- Let me make this very clear.
- It would be 3-methylnonane.
- Because the methyl group, that one carbon, that one CH3, is
- attached to the third carbon on our nonane backbone, so
- that right there is 3-methylnonane.
- Since I drew this out, what is this right here?
- Well, once again, we have this nonane backbone, one, two,
- three, four, five, six, seven, eight, nine, and you want to
- number it so that this methyl group is at the lowest number
- carbon as possible.
- So it's closer to this end than that end.
- So it's one, two, three, four, I'll do that in magenta, and
- you can keep numbering, five, six, seven, eight, nine.
- So this one is going to be four, and then you have your
- methyl group.
- It's just one carbon sitting right there, so
- 4-methylnonane.
- Now, let's go the other way around.
- Let's say we start with the name and we want to figure out
- its formula.
- And hopefully, this gives you a good understanding how
- things will get more complex.
- And over the next few videos, they'll get more and more
- complex, but you'll see it's all at
- least reasonably logical.
- So let's say I were to give you let me think of one.
- Let's say 2-propylheptane.
- So how do we take this apart?
- So the first thing you see, it is an alkane.
- It's all going to be single bonds.
- Heptane, this is kind of the core.
- So the longest chain here, hept- is the prefix for seven.
- So this tells us-- let me make this clear.
- This tells us that we're dealing with all single bonds.
- That's what the -ane tells us.
- If we had double bonds, it would be -ene,
- triple bonds, -ine.
- We're going to see that in the future, but let's stay
- simple right now.
- The hept- tells us we're dealing with seven carbons.
- And then what does this 2-propyl mean?
- Well, propyl tells us-- what was the prop- prefix?
- If methyl is one, ethyl is two, propyl is three, butyl is
- four, so this is a three-carbon group, and it's
- going to be attached to the second carbon on the heptanes.
- Let me draw the heptane chain.
- So we have seven carbons, so one, two, three, four, five,
- six, seven.
- And then on the second carbon-- just let me pick a
- good color here.
- On the second carbon, so if we just number it one, two,
- three, four, five, six, seven, on the second carbon right
- there, we have a propyl group.
- We have a propyl group, but it is a three-carbon group.
- So let me draw the propyl group.
- So we have a one, two, three, three-carbon group, and it's
- attached at the second carbon right there.
- So this molecule, 2-propylheptane
- looks just like this.
- Let's do another one, maybe one that seems a little bit
- more difficult.
- Let's say that we have 6-butyltetradecane.
- And all of these might seem a little daunting when you see
- it at first, but if you really just break it up, it actually
- is pretty logical.
- So once again, we have the -ane there, so it's all going
- to be single bonds.
- What is tetradec-?
- What is that prefix?
- Well, dec- is 10 and then we have tetra-, that's 4
- plus 10, that's 14.
- Tetradec- is 14.
- So this is telling us that we're dealing
- with a 14-carbon chain.
- Let's draw that.
- So one, two, three, four, five, six, seven, eight, nine,
- ten, eleven, twelve, thirteen, fourteen carbon chain.
- And if we number them, one, two, three, four, five, six,
- seven, eight, nine, ten, eleven, twelve, thirteen,
- fourteen, this tells us that the sixth carbon will be
- butyl, will be a butyl group.
- So let's see, the sixth carbon is right here.
- And butyl, and you should memorize this, methyl is one,
- ethyl is two, propyl is three, butyl is four, so we have a
- four-carbon group.
- So let me write this in a pink maybe.
- So this is a four-carbon group.
- When you call it an alkyl group, it's attached to
- something else.
- So on the sixth carbon, we have a four-carbon group, so
- one-- let me draw it this way.
- No, this is fine.
- Let's say we have one, two, three, four, so that is our
- butyl right there, and it's attached to the sixth carbon.
- It's attached to the sixth carbon right there.
- So this is what our molecule would look like.
- Now, let me ask you a question.
- Would you ever see a 9-butyltetradecane?
- Would you ever see a 9-butyltetradecane?
- So something where-- so let me redraw it like this.
- So a 9-butyltetradecane, so it would have butyl over here.
- One, two, three, four, one, two, three, four.
- Would you ever see a 9-butyltetradecane?
- Will you ever see that written?
- You might say, oh, yeah, Sal, you just drew it.
- And the reason why you won't ever see that written is
- because there's a better way to number it
- if it's like this.
- Instead of starting over here at one at this end, you'd want
- to start one that end.
- So instead of saying 9-butyltetradecane, you should
- number it the other way.
- You should say this is one, two, three, four, five, six.
- So this is actually also 6-butyltetradecane.
- Let me be sure I got that.
- One, two, three, four, five, six.
- So instead of starting from the left and making this the
- ninth carbon, you always want to start numbering from the
- direction that has the lowest number for the first group.