Class 12 Exam > Class 12 Videos > Chair and boat shapes for cyclohexane - Chemistry, Class 12
Chair and boat shapes for cyclohexane - Chemistry, Class 12 Video Lecture
FAQs on Chair and boat shapes for cyclohexane - Chemistry, Class 12 Video Lecture
| 1. What is the chair conformation of cyclohexane? |  |
Ans. The chair conformation of cyclohexane is a three-dimensional arrangement of the carbon atoms in a cyclohexane molecule that resembles a chair. It consists of six carbon atoms forming a ring, with each carbon atom bonded to two hydrogen atoms. The chair conformation is the most stable conformation for cyclohexane due to the minimal steric strain between the atoms.
| 2. What is the boat conformation of cyclohexane? | |
Ans. The boat conformation of cyclohexane is another three-dimensional arrangement of the carbon atoms in a cyclohexane molecule. It is called a boat because it resembles the shape of a boat. In this conformation, two carbon atoms are closer together, causing steric strain and slightly higher energy compared to the chair conformation. The boat conformation is a higher energy conformation and is less stable than the chair conformation.
| 3. What are the advantages of the chair conformation over the boat conformation in cyclohexane? | |
Ans. The chair conformation of cyclohexane has several advantages over the boat conformation. Firstly, the chair conformation is more stable due to the minimized steric strain between the atoms. Secondly, it allows for a staggered arrangement of the hydrogen atoms, reducing the torsional strain. Lastly, the chair conformation allows for easy interconversion between different conformations, making it more flexible and accommodating in chemical reactions.
| 4. How does the chair conformation of cyclohexane contribute to its physical properties? | |
Ans. The chair conformation of cyclohexane plays a significant role in determining its physical properties. Due to the chair conformation's stability, cyclohexane exists predominantly in this conformation at room temperature. The chair conformation also results in the absence of any net dipole moment, making cyclohexane a nonpolar molecule. Additionally, the chair conformation allows for efficient packing of cyclohexane molecules, leading to its relatively high melting and boiling points compared to other similar-sized compounds.
| 5. How can the chair conformation of cyclohexane be interconverted into different conformations? | |
Ans. The chair conformation of cyclohexane can be interconverted into different conformations through a process called ring flipping. Ring flipping involves the simultaneous upward or downward movement of all carbon and hydrogen atoms in the cyclohexane ring. This process results in the conversion between the two chair conformations, known as the axial and equatorial conformations. Ring flipping is a rapid process that occurs at room temperature, enabling cyclohexane to sample different conformations and exhibit its unique reactivity.
Text Transcript from Video
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--
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--
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Nov 13, 2024 Last updated |
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The content of Chair and boat shapes for cyclohexane - Chemistry, Class 12 is prepared as per the latest Class 12 syllabus.
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