For all the cyclic molecules
we've dealt with so far, we've just drawn them as rings. For example, for cyclohexane
we've literally just drawn it as a hexagon. So we've drawn cyclohexane
like that. Now, we know from the last
several videos that all the bonds for carbon don't sit
in the same plane. If we take the example
of methane, that's the simplest example. You have your carbon sitting
in the middle. You'll have kind of a hydrogen
popping out like that, another hydrogen that's in the plane
of the screen, another one that's behind the screen,
and another one that is straight up. So you kind of have this
tetrahedral structure, and in the case of methane you have
that 109.5 degree bond angles. Carbon likes to form bonds
of this shape. It won't always be
109.5 degrees. It'll be something close to
it, depending on what the different atoms or molecules
are that it is bonded to. So given that, what would a
cyclohexane molecule actually look like if we try to
visualize it in three dimensions? So to think about that, let's
think about these two bonds first. I'll try my best to
draw it in one of its three-dimensional shapes. So those bonds right there,
I will draw like that. And then this down here, in
orange, I will draw like this. And then this up here,
in magenta, I will draw like that. And then, let me see, in, in
purple, I'll do these two right over here, and I'll
draw them like this. So you have that
and like that. This hopefully makes clear that
over there is that end over there, this end over here
is this end over here, and this way that I've drawn the
cyclohexane is called a chair configuration. Chair shape. And it might be obvious. It looks like a chair. That's the back of the chair,
this is where you would sit down on the chair, and I guess
the back of your calves would go against here. Your knees would sit on it
someplace like that. That's called the chair
configuration. Now another configuration that
it could be in is called the boat configuration. And so if I were to put this
exact one in the boat configuration, if I take it
from a slightly different perspective, if I'm looking at
it, kind of, head on, it would look something like this in
the boat configuration. It would look like this. Now I want to use the purple. It would look like that. Now, the first thing you're
probably saying is, Sal, you said that the reason why it
looks like this is because carbon likes to form these kind
of tetrahedral, or this tripod shaped bonds. I don't see the tripod shaped
bonds either here or here. Let me draw that boat a little
bit, at least this end of the boat a little bit better. There you go. And you say, well I don't see
that tripod shape over there. And to see the tripod
shape, you just have to draw the hydrogens. So let me draw some
hydrogens here. So let me draw a hydrogen
here that will go straight down like this. A hydrogen that goes straight
down over here, a hydrogen that goes straight up over here,
straight up over here, straight down over here,
straight up over there. I've now drawn one hydrogen
on every carbon. And now let me draw
some hydrogens. Let me draw a hydrogen here that
goes straight up, not up really-- to the side
over here. So a hydrogen there, let me draw
a hydrogen over here that does the same thing. So those guys have
their hydrogens. A hydrogen right over here. And then, let's see, this guy
needs his hydrogens still, so he'll have a hydrogen that goes
down like that, and a hydrogen and it goes
like that. And this guy will have a
hydrogen that goes like that. And when you see it like this,
if you look at any one carbon on this molecule, if you look at
any one carbon, you can see that's forming the same
tetrahedral shape that has a tripod at every one. Over here, you have that close
to, roughly 109 degree, 110 degree angle between each of
the constituents that are bonding to the carbon. Now, I've drawn the different
hydrogens that are coming off of these carbons in different
colors, and I've done it for a purpose. The ones that are going straight
up or straight down, we call those axial hydrogens. And the ones I drew in orange
that are kind of going to the side in some level, we call
these equatorial. These are equatorial
hydrogens. And the reason why it's useful
to know that name is when we talk about the different
configurations, the different chair and boats, whether
something is equatorial or axial can change if this were to
flip up, or vice versa, and things like that. And we'll talk more about
that in the next video. And the reason why they're
called equatorial is if you think about it, and it's
sometimes hard to visualize, this bond right here is parallel
to this bond right over there. And this bond right over here
is parallel to that. It's parallel, the equatorial
bonds are parallel, to some part of the ring. So that one is parallel to
that right over there. Actually I should even, I could
even color-code that. This, well, I don't want
to use that same color. This is parallel to this and
this is parallel to that. And we could do it for all
the equatorial bonds. So for example, I don't
want to-- I'm running out of colors here. So this right here is parallel
to this, and this, and that over there. So we could keep doing
it for all of them. I could do it for the other
set right here. This guy right here
is parallel to that guy over there. I didn't quite draw it like
that, but hopefully it makes the idea clear. And I'll do one more of
these just to show what's parallel to what. This bond is parallel to that. So the ones that are parallel to
some part of the ring we're calling equatorial. And the ones that kind of jump
out of the ring, that aren't parallel to any other part
of the ring, we're calling those axial. And the way I've drawn it here,
the axials are the ones that point up and point
straight up and point straight down. We can do the same thing on
a boat configuration. Now, one question you might ask
is, well, there's these two configurations. Both of these would result in
tetrahedral type shapes at each of the carbons. In fact, let me draw
it for you. So this axial hydrogen is
pointing straight down, this one is pointing straight down. Here, this hydrogen is actually
going to point straight down because
we flipped it up. And then over here you would
have a hydrogen point straight up, and then one that's
kind of pointing down. This gives a tripod there. To have the tripod over here,
you'll have to have a hydrogen that points a little bit like
that, one that's pointing a little bit like that, along,
well, you can kind of view it along the same plane as this
guy would be parallel. It's hard to see it in
this, but he would actually parallel to that. This guy would be out like this,
and then this guy would have an axial hydrogen, and
then he would have one equatorial one just like that. So you could draw the tripod
shapes in either the chair or boat configuration. But one question is, well,
what's more stable? That's actually one of the main
points of being able to visually think about the three
dimensional structure of any of these hydrocarbons, or in
this case cyclohexane. So in this situation, we know
from past videos, that all of these carbons with their
hydrogens around them, these bonds, these have electron
clouds around them. The electron clouds are
negative, and so they want to get as far away from each
other as possible. In this chair configuration, you
have this carbon up here, the ch2 we could consider it,
has two hydrogens and is connected to the rest
of the ring. It's as far as possible from
this ch2 as possible. So in that situation, we have
a lower potential energy, or it is a more stable shape. Or more stable configuration. In the boat configuration,
this ch2 up here is much closer to this ch2, I mean,
that's really the main difference between the two. And they want to get away
from each other. They want to repel ech other. So this one will have higher
potential energy, or it will be less stable. So this is just a starting
point of how to visualize cyclic hydrocarbons and we'll
use this information in the next video to think a little
bit more about, maybe, the different chair configurations
that a molecule could have, and what could be more stable. In this situation, in the case
of just cyclohexane, the two chair configurations
are equally stable. And let me just touch
on that a second. So you have, well,
I don't have to-- actually, let me see. I won't copy and paste. I'll just redraw
the other chair configuration for this guy. Actually let me just do it
separately over here because I've made the colors
here so confusing. Let me draw two, the same
cyclohexane, but in two different chair configurations
that it could be equilibrium in. So you could have this one, you
could have this one, so this could be one chair
configuration, and I'll draw it like this. And then the same hydrocarbon
could be in-- or the same cyclohexane could be in
equilibrium with the this other chair configuration
that looks like this. Let me have a little
more space here. So it looks like this. Let me do the pink. It goes up like that,
like that. Let me make sure I'm-- no,
I want to do it actually. This pink guy goes like this. And then the blue guy is going
to be just like this. So notice, in this situation
this carbon appears kind of at the top of the chair, and this
carbon is at the bottom, and then they've flipped. But these are equally stable
configurations. But one way to think about is
all of the axial guys on this carbon here turned into
equatorial on this carbon and vice versa on the two. Let me show it to you. Let me just draw the hydrogens
on this carbon. This carbon's hydrogens has an
axial hydrogen, and has an equatorial hydrogen, whose bond
would be parallel to that just like that. And this guy would have an
equatorial hydrogen whose bond is parallel to actually
both of these guys. And an axial hydrogen. But when it flips, and I'm
just drawing those guys' hydrogens, but when this
structure flips like that, what happens? Well, this hydrogen over here
goes into this position, and this yellow hydrogen over here
goes into this position. So over here, it was
equatorial, and now it becomes axial. The same argument can
be made over here. This equatorial hydrogen, when
it flips-- when this whole blue part flips down--
now becomes axial. And this axial hydrogen, when
you flip it down, becomes equatorial. And you can actually do that
for all of the hydrogens. Over here you have an
axial hydrogen. Once you flip it, you have an
axial hydrogen, and then you have an equatorial hydrogen. When you flip it, these
two equatorial hydrogens become axial. So they become axial and then
both of these guys become equatorial. So let me do that in yellow. Both this guy and this guy
become equatorial So this and that become equatorial. They become parallel
to the other end. And you could do it for these
two hydrogens, as well. So that's another interesting
to think about. And this is really just practice
on visualizing what's going on when we when
we visualize--