So when we name organic
molecules, the core of what we think about is just how many
carbons form the chain or form the ring that we're
looking at? So let's say I have something
like this. And hopefully, you're reasonably
familiar with what this represents. And I'll review it
a little bit. So let's say I have something
like this. Let's say that that
is the molecular structure right there. And so the first question you
should be asking is how many carbons are there? And some of you might
say, wait, how is that even a molecule? And just as a review, the
end point of every line represents a carbon. So that's a carbon, that's a
carbon, that's a carbon, that's a carbon, that's a
carbon, that's a carbon. And we have one, two, three,
four, five, six carbons and we have no double bonds. So if you have all of that
information you're ready to name this molecule. And before I actually name it,
let me just kind of give you all of the different prefixes. So if you have one carbon,
the prefix is meth-. If you have two carbons,
the prefix is eth-. And it's good to memorize
at least up to about 10. And actually it kind of
repeats after that. If you have three carbons,
the prefix is prop-. Prop- like propane, and you've
heard of ethane and methane. So you'll see all
of that soon. Four, you're talking
about but-. Five, and after five it kind
of becomes the traditional prefixes that we associate with
a lot of these numbers. So at five, it's pent-,
like pentagon. Six, it's hex- like hexagon. Seven is hept-. Eight is oct-, like octagon. Nine is non-. Ten is dec-. And then after that it kind of
starts to have a pattern here, and you're not going to really
deal with things much beyond the teens, but I'll just write
them down here just out of interest. Eleven is undec-. And for those of you who know
French, I'm not one of them, but I know that one in French
is une, or in Spanish, uno. So it's 1 and 10, 11. Twelve is dodec-. Do or dos, if you're speaking
Spanish, for 2. Dec for 10, 2 and
10, that's 12. Thirteen, you could imagine
what it's going to be. It is tridec-. Fourteen is tetradec-. A tetrapod is something
with four legs. And after that it, becomes
very systematic. At fifteen is pentadec-. Notice pent-, 5 and 10. Sixteen is hexadec-. Seventeen is heptadec-. So it just goes on
and on and on. I don't think I've got to go--
anyway, it's hexadec-, heptadec-, octodec- is
eighteen, nineteen is nonadec-, and then twenty
is actually iso-. But we won't even
go into that. This'll probably serve
our purposes. I mean, I could go up to
sixteen is hexadec-. So this is just how
many carbons are in our longest chain. What I drew here is
just one chain. So we could immediately--
let's try to name it. Well, how many carbons
do we have here? Well, we have one, two, three,
four, five, six carbons. So we'll be dealing with
hex- as a prefix. And then to get, I guess, the
post-fix on this prefix, or the kind of the root, you look
to see if there are any double bonds here. And there are no double
bonds here. And if we have no double bonds
in this carbon chain, we're dealing with an alkane. This is called an alkane, which
is a general term for all of the chains of carbons
that have no double bonds on them, or no triple bonds,
all single bonds. So in this situation, you take
hex- for six, so this is hex-. And then, because it's
an alkane, it gets the -ane from alkane. So this is hex-,
this is hexane. Let's do another one. Let's say I have this
thing right here. I'll draw-- let's make
it even longer. So let's say I have that
thing right there. So how many carbons
do we have? We have one, two, three, four,
five, six, seven carbons. They're all single bonds,
so it's an alkane. So this will be seven carbons. It is heptane because we
have all single bonds. Now, if things form a chain,
or if things form a ring, I should say, we put the prefix
cyclo- in front of it. So if I have-- let me show you
what I'm talking about. So if I just have five carbons,
one, two, three, four, so one, two, three,
four, five. OK, so that's five
right there. I have one, two, three, four,
five carbons in a chain. If I just have five carbons in
a chain like this, this would be pentane. But if I have five carbons
and they form a ring, so let me draw it. So it's one, two, three,
four, five carbons and it forms a ring. Let me make the drawing
a little bit better. So it's really, I'm just
drawing a pentagon. But notice, this has
five carbons on it. I can draw the carbons here. Carbon, carbon, carbon,
carbon, carbon. And just as a review, what you
don't see is the hydrogens they're bonded to. Each of these guys have two
bonds, so they must have two bonds with something else and
those are going to be with hydrogen, And I'lll draw it here just as
a bit of a review, but you notice very quickly, the drawing
gets extremely messy when you draw the
two hydrogens on each of these carbons. So it's a little bit
over-- maybe I shouldn't be doing that. But there you go. So it becomes very messy when
you draw the hydrogens, so it's better to just assume
that they're there. If we don't draw all four bonds
of the carbon, the other two bonds are going to
be with hydrogen. So here, you might say, OK, this
is an alkane, because I don't have any double
bonds here. All of these are single
bonds with the carbon. I have five carbons, so you
might say this is pentane, but you have to think about
one more thing. It's in a ring, so we add
the prefix cyclo- to it. So this is, because it's a ring,
we write cyclopentane. So let me just break
that apart. This tells us that we're
dealing with a ring. You see that this is
a ring right there. This tells us that we're dealing
with five carbons, and then this tells us right here,
the -ane part, that tells us that they are all
single bonds. All carbon-carbon
single bonds. No double or triple bonds. All single bonds. So let's go the other way. Let's start with the word and
let's see if we can figure out what the actual structure
would look like. Let's say I have cyclononane. So what is this telling me? This tells me I'm dealing
with a ring. That is a ring. It's going to have
a ring structure. It's going to have nine carbons,
nine C's, and then it's an alkane, so they're all
going to be single bonds. So if I want to draw it, I want
to draw nine carbons in a ring, it's not a trivial
thing to draw. I'll try my best, so let's see,
that's one, two, three, four, five, six, seven, eight. Let's see, let me draw it. I'll try a little a
better shot at it. So, let's see, you have one,
two, three, four, five, six, seven, eight, and then nine. And then you can connect the
last. So let me make sure that this is-- and obviously, I could
have drawn it better than that, but hopefully, you
can see all of the edges here. So I have one, two, three, four,
five, six, seven, eight, nine carbons. It's in a cycle. It's in a ring. I have nine carbons. They're all single bonded, so
this is cyclononane, although there's probably better ways to
draw that ring right there. So if someone were to tell you,
octane, and that word might feel familiar to you
from the gas station. They are literally talking about
the molecule octane. And now you know, or at least
you have a sense of what they're talking about. The oct- tells you that you
have eight carbons. There's no cyclo- in front of
it, so it's not a cyclo. It's just going to be a chain. And then the -ane part tells
you that they're all single bonds, so it's just going to be
eight carbons in a chain. One, two, three, four, five,
six, seven, eight. It's just going to
look like that. One, two, three, four, five,
six, seven, eight. In the next few videos, we'll
add more to these molecules and make the names even
more complex.