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Current time:0:00Total duration:5:44

So here's a picture of
the cubane molecule, which is an alkane that's
shaped like a cube. And for that reason, it's
one of my favorite molecules. I just think it's
really cool looking. And you can see that at each
of the corners of the cube, there's a carbon. So there are eight
carbons total. And then there's also
a hydrogen coming off of each of those carbons for
a molecular formula of C8H8. At first, a lot
of chemists didn't think this molecule could be
made because of the high amount of angle strain that's
present in this molecule. But it was made
starting in the 1960s. And it's being looked at
for a lot of potential uses in medicine and
explosives these days, and because you can
nitrate it and make things like octanitrocubane and
heptanitrocubane, which are potential explosives
for the future. And we're going to look and
see if we can name cubane using IUPAC nomenclature
in this video. So let's first think about the
rules we learned in the video on bicyclic nomenclature. And if you're
trying to figure out how many rings
are in the system, you have to make
cuts and figure out how many cuts does it take to
get to an open chain alkane. So if we start with this yellow
version of cubane over here on the left, I'm going
to start cutting bonds. And let's see how
many cuts it takes to get to an open chain alkane. For example, I could start
by cutting right here. So we'll say that's
our first cut. And then our second cut, we
could make a cut right back here like that. So we could make that my
second cut here on my cubane. And then for my third cut, I'm
going to go for this one right up here. So we'll take care of that one. So that's three cuts so far. And then, if I just go ahead
and take out of this one, this bond right here, and then
this bond right here, so that's cuts four and five. I now get an open chain alkane. So it took five cuts
for us to do that. So there are five rings in
cubane, so it's pentacyclo. So that's just not immediately
obvious, to me anyway, as to why there are
five rings in cubane. So let's go ahead
and write pentacyclo to start the IUPAC name here, so
pentacyclo, meaning five rings. And then we start our brackets,
just like we did in the video on bicyclic nomenclature. And to finish
naming cubane, we're going to pretend like it
is a bicyclic compound. And the first thing
we do is identify our bridgehead carbons. So the carbons that are common
to both of the two rings here. So hopefully it's obvious
those are two rings and those are the
bridgehead carbons that connect those two rings. When you number a
bicyclic compound, you start at one of
the bridgehead carbons and then you go the
longest path first. So I'm going to
start at this carbon, and I'm going to go the longest
path, which would be up here. So this would be
number 2, this would be number 3, carbon
number 4, carbon number 5, carbon number 6, which takes me
to the other bridgehead carbon. And then you name your
next longest path. So I'm just going to continue
around and make this carbon 7, and then make this one
back here carbon 8. So those are my eight
carbons of cubane. And so, once again,
I can continue to pretend like it's
a bicyclic molecule. And the next thing
I would do is I would name the number of
carbons in my longest path. So the number of carbons
in my longest path would be this one, so there'd
be 1, 2, 3, 4 carbons. Remember, you exclude
the bridgehead carbons when you're doing this, so we're
going to start with a 4 right here, like that. Next, you do the
number of carbons in your second longest path. So we can see my
second longest path would be this one right here. And there are two carbons
in my second longest past. So I go ahead and put a
2 over here like that. And then finally,
it's the number of carbons between the
bridgehead carbons, which in this example,
of course, there are no carbons between my
two bridgehead carbons. So I would put a
0 here like that. But of course, cubane is
not a bicyclic compound, so we have to keep going. We have to figure out how I can
continue naming this molecule. And the way to do
it is to next think about how many carbons are
there between carbons 2 and 5. So if I draw a
dashed line in here, so I can pretend like
I'm connecting those two right there. And of course, there are
no carbons between 2 and 5. So I can keep going. I could make this is 0, and
I could put a 2 comma 5, saying there are no carbons
between carbons 2 and 5. And I can continue on. I can do that
between the 3 and 8. So if I were to connect the 3
and the 8 back here like that, there are no carbons
between 3 and 8, so I can write 0,
and then 3 comma 8. And, of course, I can do
the same thing over here on the right. So between 4 and 7
there are no carbons. So I can write 0,
4, and 7, like that. So let me just clear
up that 7 there. And we're done
with our brackets. So the last thing you
need to do when you're naming a polycyclic
alkane like this is to figure out how many total
carbons are in the molecule. Well, of course, there
are 8 So this is octane. So I can go ahead and write
octane down here, like that. And I have my IUPAC
name for cubane. It is
pentacyclo[4.2.0.0(2,5).0(3,8)0(4,7)]octane. And there are several
other molecules that are similar
to cubane, which are also very interesting. So molecules like
dodecahedrane would be one to check out as well if you
like the structure of cubane.