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[SQUEAKING]
[RUSTLING] [CLICKING]

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SARAH HEWETT: All
right, good afternoon.

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We should get
started, because we

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have a lot to talk about today.

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So today is the second in
a series of three lectures

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about the essential oil lab.

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You'll get a third
lecture and a little bit

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about X-ray crystallography.

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But today, we're going
to finish talking

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about the main synthetic
parts that you'll be

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doing in the essential oil lab.

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So today, we're going
to talk about how

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if your separation worked.

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And before I get
too far into that,

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there was a question
in the Tuesday lecture

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about the naming of terpenes.

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And so if you
remember, the terpenes

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come from the
isoprene structure,

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which was five carbons
and eight hydrogens.

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But then there are some
terpene derivatives,

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like menthol, that
don't necessarily

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have that five carbon,
eight hydrogen structure.

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So this obviously has an O-H
group and more hydrogens.

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And so what I found
in the literature

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is that there are
terpenes, which

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follow the strict pattern.

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And then there are
terpenoids, which

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are derivatives of terpenes.

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They are synthesized
from the same backbone.

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But then they get extra
hydrogenation or oxidation

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done to them.

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So, like, your carvone has
the oxygen double bond in it.

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So that's technically
a terpenoid.

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They seem to be referred
to pretty interchangeably

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in the literature, which
I thought was interesting.

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But that is probably
the more accurate way

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to name these
types of compounds.

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So hopefully, that clears up a
little bit of that confusion.

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So jumping in to the rest of the
essential oil lab, on Tuesday,

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we talked about
what you're going

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to do on day one
of the lab, which

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is you'll get your essential
oil, which will either

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be spearmint oil or caraway
oil, and you will separate it

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into its two major components,
which are your carvone, there

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on the left, and your limonene.

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So essentially, you'll take
an oil that looks like that,

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and you'll separate it into
two other oils that will also

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look really similar
to that first one,

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except hopefully,
they're pure compounds.

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So if you do your vacuum
distillation really well,

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and you separate those, and
you get two pure compounds,

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we need to figure out how to
characterize your separation,

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and figure out how well you were
able to separate your carvone

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from your limonene.

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And we're going to do that
in a whole number of ways.

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You'll get a lot of experience
with different analytical

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techniques.

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And these are the major
methods that we're

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going to be using
to characterize

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the success of your separation.

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So we'll be doing refractometry,
gas chromatography,

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infrared spectroscopy,
polarimetry,

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and X-ray crystallography.

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And so today,
we're going to talk

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about the first four of those.

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And then, like I said,
in a week or two,

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Peter Muller from the
X-ray crystallography lab

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will come and do a much more
detailed explanation of X-ray

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crystallography and
what information you

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can get from that.

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So to start with,
refractometry--

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refractometry is a way to
measure the refractive index

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of a compound.

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And that is a
characteristic property

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of different compounds.

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And it is-- it comes from the
ratio of the velocity of light

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and air to the velocity
of light in a liquid.

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So you have your light
traveling through the air.

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Then it hits the liquid
and it slows down,

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and it changes the angle.

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So you'll notice, if you
ever look through some water,

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you'll know that the image
is slightly distorted.

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And that is because of water
having a different refractive

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index, or water having--

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the light slows down as it
travels through the water.

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So all of our organic
liquids-- so like I said,

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you're going to be separating
your oil into two other oils.

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So we'll have liquids, which
means that they will have

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refractive indices as well.

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And most organic liquids
will have a refractive index

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somewhere from 1.3 to 1.7.

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And the way that you calculate
that is it's represented as n.

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And you can either do
the ratio of the velocity

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of the light in the
air to the velocity

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of the light in the liquid.

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But that is hard to measure.

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So in the lab, we can
measure the angles

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at which the light travels.

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So if you have light that
is coming through the air--

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so if this part is the air,
and you have your light,

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it'll hit your liquid
interface at a certain angle,

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which is theta from
straight up and down.

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And then, it'll get refracted
at a different angle.

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We call that theta prime.

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So you can measure
that in the lab

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and calculate your
refractive index.

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The refractive index is
dependent on the wavelength

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of light.

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So you might imagine that
if the refractive index

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and how much this angle--

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and how much the speed
of the light changes

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is dependent on how the light
interacts with your liquid,

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then it'll depend on the
properties of your light-- so

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the wavelength-- and the
properties of your liquid.

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And one that we care
about is the density.

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So the way that we
account for this

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is that we have the
refractive index.

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And we call it
refractive index D20.

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And so D represents that you use
light from the sodium D line.

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So if you remember from,
maybe, gen chem or physics,

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if you heat up an element
very hot so it emits light,

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you can--

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each element has a
characteristic set

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of wavelengths of
light that it emits.

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And sodium's happens
to be around--

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its brightest emission happens
to be around 586 nanometers.

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So if you use a sodium lamp,
and you can select for these 586

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nanometers, then you get a
characteristic one wavelength

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of light that you can
pass through your sample.

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So you know what
the wavelength is,

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and you can know that
you're just getting

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that one wavelength of light.

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And then, you want to make
sure that all of your samples--

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or your measurements are taken
at 20 degrees Celsius so that

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the density of your liquid.

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So if you change
the temperature,

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you change the density.

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So we'd make all
of our measurements

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at 20 degrees Celsius.

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And here are the approximate
refractive indices

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of limonene and carvone.

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And you can find
different values for them

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in the literature, because
the compounds that they

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used to measure these
in the literature

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are of different purities.

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So you can by limonene and
carvone at 95%, or 96%,

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98% purity.

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And depending on
what purity you use,

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you'll get a slightly
different value.

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But they should be
within that range.

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And when we measure
them in the lab,

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we go out to four
decimal places.

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The way that we'll
do this in the lab

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is with the refractometer.

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And this is a picture of the
refractometer in the lab.

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And this part over here is
the prism or the crystal.

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And so you'll put
your liquid sample--

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you just put a few drops
right on the crystal.

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And then, you close the lid and
the refractometer instrument

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shines light
through your sample.

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It can measure-- it knows
what angle the light is

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hitting the sample at.

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And then it can measure how
much light it gets back out.

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So it'll change the angle
of the incident light

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until it gets total internal
reflectance until it

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reaches the critical angle.

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You remember from physics?

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And so once it figures out
what the critical angle is,

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then it can figure out
the refractive index

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of your sample.

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And so it'll tell you what the
refractive index is right here.

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You don't even really
have to do any math.

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And it'll also tell you
what the temperature is.

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So you want to make sure that
it's stabilized at 20 degrees

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before you actually
take your measurement.

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And that's about it.

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So it's a pretty easy
measurement to take,

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but it will help you to identify
the purity of your compounds,

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because the
refractive index is--

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we can think of it as a
linear quantity made up

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of the refractive indices
of the two substances

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that we have in our mixture,
multiplied by their molar

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fraction.

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So your refractive
index of a mixture

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is the sum of the
refractive index

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of pure limonene times your
mole fraction of your limonene,

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plus your refractive index of
your carvone times your molar

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fraction of your carvone.

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And so that you don't have to
sell for a million variables,

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if you remember
the mole fraction,

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mole fractions have
to add up to 1.

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So your mole
fraction of limonene

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is 1 minus your mole
fraction of carvone.

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So you can plug that in up there
and, using the measurements

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that you take in
the lab, you can

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solve for the mole
fractions of each

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of these components in
both of your fractions

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that you collect from
your distillation.

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And you can determine
their purity that way.

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So another way to determine the
purity of your-- or fractions

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that you've collected is
through gas chromatography.

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And this is a picture of the
GC instrument in the lab.

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And it's right next to the
ICPMS, so you may have seen it

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if you were in lab yesterday.

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And if not, you can take
a peek and see it today.

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So this is the
instrument itself.

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This is the autosampler.

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So you guys will make
your sample vials,

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put them in up here, and then
it'll pick them up, put them

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into the instrument, and
then it'll automatically

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inject the sample for you,
which is kind of nice.

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And then this
thing over here, it

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generates hydrogen
and air, which

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are used in the detector
of the instrument.

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So the way that
gas chromatography

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works, if you wanted to take
a peek inside the instrument

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in a very, very
simplified fashion,

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you have a carrier gas,
which in our case is helium.

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And the carrier gas,
if you think about-- so

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this is a type of
chromatography.

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And you guys did chromatography
in the ferrocene lab

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with your thin layer
chromatography and your column

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chromatography.

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So in your TLC and in your
column chromatography,

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what was your stationary phase?

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AUDIENCE: Alumina?

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SARAH HEWETT: Alumina, yes.

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So you had your alumina, and
it was coated on the TLC plate.

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Or you packed your
column with the alumina,

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and that's your
stationery phase.

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And then, what was
your mobile phase?

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AUDIENCE: Hexanes
and ethyl acetate?

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SARAH HEWETT: Hexanes
and ethyl acetate.

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And you guys made
different mixtures of those

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to determine the best
separation of your compound.

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So in thin layer chromatography
and in column chromatography,

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which of those phases had
a bigger determination

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on the separation of
your two components?

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AUDIENCE: The mobile phase?

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SARAH HEWETT: The
mobile phase, yeah.

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So you could change
the polarity and it

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would change the separation.

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In gas chromatography,
it's kind of the opposite.

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So you have your carry your gas.

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And that's going to
be your mobile phase.

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So that'll help push your
compounds through the column.

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And then the column is
your stationary phase.

248
00:09:50,890 --> 00:09:53,190
And you can change
the properties

249
00:09:53,190 --> 00:09:55,680
of your stationary phase
in order to separate--

250
00:09:55,680 --> 00:09:58,890
get different types
of separation.

251
00:09:58,890 --> 00:10:03,330
So there are two major
types of compounds that they

252
00:10:03,330 --> 00:10:06,270
use in column chromatography.

253
00:10:06,270 --> 00:10:09,300
And the first one, this is--
anyone know what this is?

254
00:10:13,900 --> 00:10:21,242
Polyethylene glycol,
which is something

255
00:10:21,242 --> 00:10:22,450
you may have heard of before.

256
00:10:22,450 --> 00:10:24,990
So these are your ethyl
groups, and then the glycol,

257
00:10:24,990 --> 00:10:26,770
because it's got alcohol groups.

258
00:10:26,770 --> 00:10:30,990
And so this notation is
the notation for a polymer.

259
00:10:30,990 --> 00:10:32,670
So the way that
this is written is

260
00:10:32,670 --> 00:10:35,460
you could have any number
of this repeating unit

261
00:10:35,460 --> 00:10:38,130
until the end.

262
00:10:38,130 --> 00:10:40,390
And this is a polar
stationary phase.

263
00:10:40,390 --> 00:10:42,810
So if you're trying to
separate compounds that

264
00:10:42,810 --> 00:10:44,940
have differences-- large
differences in polarity,

265
00:10:44,940 --> 00:10:47,190
a lot of times you'll
use the polar compound.

266
00:10:47,190 --> 00:10:50,593
Because it has these oxygens
that have their lone pairs.

267
00:10:50,593 --> 00:10:52,260
So it can interact
with polar compounds,

268
00:10:52,260 --> 00:10:55,140
it can form hydrogen bonds,
all kinds of neat stuff.

269
00:10:55,140 --> 00:10:58,050
But the one that we're
going to use in the lab

270
00:10:58,050 --> 00:11:00,570
is this compound here.

271
00:11:00,570 --> 00:11:02,460
And it is called a polysiloxane.

272
00:11:09,730 --> 00:11:13,130
So polysiloxane-- and it has
these silicon groups that

273
00:11:13,130 --> 00:11:14,540
have to methyl groups attached.

274
00:11:14,540 --> 00:11:18,470
And another name for this
particular-- so polysiloxane

275
00:11:18,470 --> 00:11:22,353
is the overarching name for
this class of compounds.

276
00:11:22,353 --> 00:11:24,020
This one has two
methyl groups attached.

277
00:11:24,020 --> 00:11:27,650
So one of the other names
for it is dimethicone.

278
00:11:27,650 --> 00:11:29,720
I don't know if you've
heard of that before.

279
00:11:29,720 --> 00:11:31,280
It's in a lot of things.

280
00:11:31,280 --> 00:11:34,430
They use it extensively
in lotions, shampoos,

281
00:11:34,430 --> 00:11:35,585
and sometimes in food.

282
00:11:35,585 --> 00:11:38,210
It prevents foaming and it makes
things feel nice and slippery.

283
00:11:38,210 --> 00:11:44,840
So that's why they use it in a
lot of cosmetics, and lotions,

284
00:11:44,840 --> 00:11:45,540
and everything.

285
00:11:45,540 --> 00:11:47,690
So the next time
you're in the bathroom,

286
00:11:47,690 --> 00:11:49,565
you can take a look at
some of your products.

287
00:11:49,565 --> 00:11:51,545
And you may see dimethicone.

288
00:11:56,780 --> 00:11:58,590
And now you know
what it looks like.

289
00:11:58,590 --> 00:12:00,140
And we're going to
use it in the lab

290
00:12:00,140 --> 00:12:02,660
to help separate your
limonene and your carvone

291
00:12:02,660 --> 00:12:06,530
to see how pure
your separation was.

292
00:12:06,530 --> 00:12:10,190
And the GC column
looks like this.

293
00:12:10,190 --> 00:12:13,420
So it's represented in this
diagram as a curled up circle.

294
00:12:13,420 --> 00:12:15,890
And so this is actually
what it looks like.

295
00:12:15,890 --> 00:12:19,040
So this is an old column taken
out of the GC in the lab.

296
00:12:19,040 --> 00:12:20,980
And you can see that
it's very, very thin.

297
00:12:20,980 --> 00:12:22,593
So this is a capillary column.

298
00:12:22,593 --> 00:12:24,010
So this is actually
a hollow tube.

299
00:12:24,010 --> 00:12:26,930
And your sample will travel
through this tube around,

300
00:12:26,930 --> 00:12:27,790
around, around.

301
00:12:27,790 --> 00:12:30,676
Does anyone have a guess
about how long this is?

302
00:12:30,676 --> 00:12:31,560
AUDIENCE: Long.

303
00:12:31,560 --> 00:12:32,352
SARAH HEWETT: Long.

304
00:12:32,352 --> 00:12:36,420
[LAUGHS] Yeah, so this is 30
meters of capillary tubing

305
00:12:36,420 --> 00:12:37,800
all wrapped up here.

306
00:12:37,800 --> 00:12:39,750
And on the inside of
the capillary tubing,

307
00:12:39,750 --> 00:12:44,520
it is coated with this
polysiloxane mixture which

308
00:12:44,520 --> 00:12:47,790
will interact with your sample.

309
00:12:47,790 --> 00:12:51,870
And it'll help cause
the separation.

310
00:12:51,870 --> 00:12:56,170
So your sample gets inserted
into the injector port.

311
00:12:56,170 --> 00:12:57,850
This is an oven, so
it gets heated up.

312
00:12:57,850 --> 00:13:00,140
And you can change the
difference in the temperature.

313
00:13:00,140 --> 00:13:01,807
And so the difference
in the temperature

314
00:13:01,807 --> 00:13:05,570
will change the amount of
separation that you get.

315
00:13:05,570 --> 00:13:08,342
So if you do it hotter,
then your compounds

316
00:13:08,342 --> 00:13:10,300
will travel through
faster, and you don't maybe

317
00:13:10,300 --> 00:13:11,475
get as good of a separation.

318
00:13:11,475 --> 00:13:12,850
If you cool it
down a little bit,

319
00:13:12,850 --> 00:13:14,110
then you tend to get
better separation,

320
00:13:14,110 --> 00:13:15,812
but sometimes it can
broaden your peaks.

321
00:13:15,812 --> 00:13:17,020
So there's a trade-off there.

322
00:13:17,020 --> 00:13:19,120
We have already made
a program for you

323
00:13:19,120 --> 00:13:21,390
that optimizes the separation
of the two compounds

324
00:13:21,390 --> 00:13:22,640
that you guys are looking for.

325
00:13:22,640 --> 00:13:24,223
So you don't have
to worry about that.

326
00:13:24,223 --> 00:13:26,177
You'll just make up
your sample, inject it,

327
00:13:26,177 --> 00:13:28,760
it'll go through the column, and
then it reaches the detector.

328
00:13:28,760 --> 00:13:30,470
And we use a flame
ionization detector.

329
00:13:30,470 --> 00:13:33,593
So that hydrogen in the
air, they get lit on fire.

330
00:13:33,593 --> 00:13:36,010
The stuff that comes out of
the column goes into the fire.

331
00:13:36,010 --> 00:13:38,200
It gets lit on fire,
it produces ions,

332
00:13:38,200 --> 00:13:42,430
and then the ions are detected
by the detector, changes

333
00:13:42,430 --> 00:13:43,960
the electrical current.

334
00:13:43,960 --> 00:13:47,582
And that is what
gives you your signal.

335
00:13:47,582 --> 00:13:49,040
This is a very
sensitive technique.

336
00:13:49,040 --> 00:13:51,260
So you do not need to prepare
very concentrated amounts

337
00:13:51,260 --> 00:13:51,720
of samples.

338
00:13:51,720 --> 00:13:53,637
So we're not going to
inject your oil straight

339
00:13:53,637 --> 00:13:54,890
into the instrument.

340
00:13:54,890 --> 00:13:57,230
You are going to do what's
called a double dilution.

341
00:13:57,230 --> 00:13:59,350
So you will take 50
microliters of your sample

342
00:13:59,350 --> 00:14:01,850
in one of those micropipettes
that you guys have been using.

343
00:14:01,850 --> 00:14:03,530
You'll dissolve it in 1
milliliter of pentane,

344
00:14:03,530 --> 00:14:05,730
so you're already making
a very dilute solution.

345
00:14:05,730 --> 00:14:08,013
And then you'll take 50
microliters of that solution,

346
00:14:08,013 --> 00:14:10,430
and you will dissolve it in
another milliliter of pentane.

347
00:14:10,430 --> 00:14:13,235
And that's what you will
inject into the GC instrument.

348
00:14:13,235 --> 00:14:14,610
Your TAs will help
you with that.

349
00:14:14,610 --> 00:14:17,910
But that's just to show you that
it is a very, very sensitive

350
00:14:17,910 --> 00:14:18,410
technique.

351
00:14:18,410 --> 00:14:22,130
So you do not need
a lot of volume.

352
00:14:22,130 --> 00:14:27,320
This is what the output
of the GC looks like.

353
00:14:27,320 --> 00:14:30,230
And you will get your
GC chromatograph.

354
00:14:30,230 --> 00:14:36,320
And the units on this are in
abundance and time in minutes.

355
00:14:36,320 --> 00:14:40,985
And so you can see that this is
a GC chromatograph of the oil

356
00:14:40,985 --> 00:14:42,110
before it's been separated.

357
00:14:42,110 --> 00:14:44,030
So it has two major
components and a couple

358
00:14:44,030 --> 00:14:46,010
of smaller impurities.

359
00:14:46,010 --> 00:14:49,580
And hopefully, if you guys do
your distillation correctly,

360
00:14:49,580 --> 00:14:50,720
then you'll get--

361
00:14:50,720 --> 00:14:53,193
your fractions will
look like there's not

362
00:14:53,193 --> 00:14:54,860
very much of one and
a lot of the other,

363
00:14:54,860 --> 00:14:58,758
and then vice versa for your
limonene and your carvone.

364
00:14:58,758 --> 00:15:00,800
And the way that you can
tell which peak is which

365
00:15:00,800 --> 00:15:05,360
is that-- so this column
is pretty non non-polar,

366
00:15:05,360 --> 00:15:06,080
like I said.

367
00:15:06,080 --> 00:15:08,450
And the interactions
with the column

368
00:15:08,450 --> 00:15:11,270
are what separates your mixture.

369
00:15:11,270 --> 00:15:13,910
But the way that it
is separated is mostly

370
00:15:13,910 --> 00:15:14,910
through boiling point.

371
00:15:14,910 --> 00:15:16,678
So when you heat
this compound up--

372
00:15:16,678 --> 00:15:19,220
and we'll talk about it a little
bit more in the next slide--

373
00:15:19,220 --> 00:15:20,735
but it'll travel
through the column.

374
00:15:20,735 --> 00:15:23,360
So things that are more volatile
will travel through the column

375
00:15:23,360 --> 00:15:25,250
faster, so things with
lower boiling point.

376
00:15:25,250 --> 00:15:26,450
And then, things with
a higher boiling point

377
00:15:26,450 --> 00:15:27,920
stay on the column for longer.

378
00:15:27,920 --> 00:15:32,910
So you can use boiling
point to sort of identify

379
00:15:32,910 --> 00:15:34,745
your compounds.

380
00:15:34,745 --> 00:15:36,120
And you also get
this information

381
00:15:36,120 --> 00:15:37,920
at the bottom, which tells
you the retention times

382
00:15:37,920 --> 00:15:39,128
of your peaks in the minutes.

383
00:15:39,128 --> 00:15:41,430
And then, it'll also tell
you the area of your peak.

384
00:15:41,430 --> 00:15:44,320
And you can use the percent
area to calculate your percent

385
00:15:44,320 --> 00:15:44,820
purity.

386
00:15:44,820 --> 00:15:48,060
So in this case, we have 41%
of one and 57% of the other.

387
00:15:48,060 --> 00:15:49,770
So it is not a very pure sample.

388
00:15:49,770 --> 00:15:52,590
And hopefully, yours will get on
the order of-- you can get well

389
00:15:52,590 --> 00:15:54,750
above 90% separation.

390
00:15:54,750 --> 00:15:57,182
So that'll give you
an idea of how well

391
00:15:57,182 --> 00:15:58,140
your distillation went.

392
00:16:01,340 --> 00:16:02,980
So some things about
gas chromatography

393
00:16:02,980 --> 00:16:05,480
that are important to note is
that you can't really identify

394
00:16:05,480 --> 00:16:06,630
an unknown without a standard.

395
00:16:06,630 --> 00:16:08,420
So if you just-- if you don't
know what your compound is

396
00:16:08,420 --> 00:16:10,160
already and you
inject it into the GC,

397
00:16:10,160 --> 00:16:11,660
all you're going to know
is that retention time.

398
00:16:11,660 --> 00:16:14,090
It doesn't give you any
information about its structure

399
00:16:14,090 --> 00:16:15,200
or anything else.

400
00:16:15,200 --> 00:16:17,312
So you can compare
retention times.

401
00:16:17,312 --> 00:16:18,770
Those are consistent
as long as you

402
00:16:18,770 --> 00:16:21,140
use the same method,
and the same column,

403
00:16:21,140 --> 00:16:22,310
and the same carrier gas.

404
00:16:22,310 --> 00:16:25,430
But you need to have a standard
that you can compare it to.

405
00:16:25,430 --> 00:16:28,048
Or if you know that there's
two components in your mixture,

406
00:16:28,048 --> 00:16:30,590
if you know what's in them, then
you can tell which is which,

407
00:16:30,590 --> 00:16:32,120
again, by their boiling point.

408
00:16:32,120 --> 00:16:33,620
So it is very useful
for determining

409
00:16:33,620 --> 00:16:35,960
the purity or the percent
composition of a sample, which

410
00:16:35,960 --> 00:16:37,550
is what we're going
to use it for.

411
00:16:37,550 --> 00:16:39,290
And like I said,
separation is determined

412
00:16:39,290 --> 00:16:41,930
by your stationary phase.

413
00:16:41,930 --> 00:16:44,370
And the stationary phase is
a liquid coating on there.

414
00:16:44,370 --> 00:16:50,270
So when you're using
GC chromatography,

415
00:16:50,270 --> 00:16:52,850
you want to make sure that you
pick a stationary phase that

416
00:16:52,850 --> 00:16:54,500
matches the type of compound
that you're separating.

417
00:16:54,500 --> 00:16:56,167
So we're going to use
this non-polar one

418
00:16:56,167 --> 00:16:59,120
because our compounds
are relatively non-polar.

419
00:16:59,120 --> 00:17:01,370
But you'll see it
used in extensively

420
00:17:01,370 --> 00:17:02,340
in other applications.

421
00:17:02,340 --> 00:17:04,132
So if you're doing a
lot of polar compounds

422
00:17:04,132 --> 00:17:06,090
with a lot of oxygen
groups or nitrogen groups,

423
00:17:06,090 --> 00:17:08,210
then you may want to use
a more polar compound.

424
00:17:08,210 --> 00:17:10,640
You can also get chiral
stationary phases that

425
00:17:10,640 --> 00:17:12,800
will help separate enantiomers.

426
00:17:12,800 --> 00:17:13,839
There's all kinds.

427
00:17:13,839 --> 00:17:17,119
If you go on any of the
Agilent website or anything,

428
00:17:17,119 --> 00:17:19,160
you can get a whole
list of different types

429
00:17:19,160 --> 00:17:21,410
of stationary phases with
different types of polarity.

430
00:17:21,410 --> 00:17:24,680
You can substitute these methyl
groups out for other things

431
00:17:24,680 --> 00:17:29,120
depending on what application
you're trying to use it for.

432
00:17:29,120 --> 00:17:30,970
And so the way that
we can characterize

433
00:17:30,970 --> 00:17:33,430
the efficiency of the separation
is by theoretical plates.

434
00:17:33,430 --> 00:17:34,900
And we mentioned this
really, really briefly when

435
00:17:34,900 --> 00:17:36,525
we were talking about
the distillation.

436
00:17:36,525 --> 00:17:38,830
So if you remember,
there was the grow column

437
00:17:38,830 --> 00:17:40,635
versus the simple distillation.

438
00:17:40,635 --> 00:17:42,010
So you get better
separation when

439
00:17:42,010 --> 00:17:44,920
you have more and more of those
cycles where the vapor can

440
00:17:44,920 --> 00:17:46,420
vaporize and recondense.

441
00:17:46,420 --> 00:17:49,400
Does that sound
vaguely familiar?

442
00:17:49,400 --> 00:17:50,193
Good.

443
00:17:50,193 --> 00:17:52,610
So essentially, that's what's
happening in this GC column.

444
00:17:52,610 --> 00:17:54,900
So you have a liquid coating
on the inside of this tube.

445
00:17:54,900 --> 00:17:56,733
And your compounds are
traveling through it.

446
00:17:56,733 --> 00:17:59,030
And they can be heated
up so they'll repeatedly

447
00:17:59,030 --> 00:18:01,250
dissolve and then
revaporize in the liquid.

448
00:18:01,250 --> 00:18:03,710
And the more times they
can do that as they travel

449
00:18:03,710 --> 00:18:07,520
through this 30 meters of
column, the more efficient

450
00:18:07,520 --> 00:18:10,120
your separation is going to be.

451
00:18:10,120 --> 00:18:12,370
And we can calculate
that using a measure

452
00:18:12,370 --> 00:18:14,160
called theoretical plates.

453
00:18:14,160 --> 00:18:15,910
And it is based on the
idea that one plate

454
00:18:15,910 --> 00:18:19,180
is one equilibrium between
the liquid in the vapor

455
00:18:19,180 --> 00:18:21,730
phase, or one of those
vaporization recondensation

456
00:18:21,730 --> 00:18:22,732
cycles.

457
00:18:22,732 --> 00:18:24,690
So you can refer to the
temperature composition

458
00:18:24,690 --> 00:18:26,460
diagrams from the
last lecture if you

459
00:18:26,460 --> 00:18:29,490
want to get a refresher on
what I mean by the vaporization

460
00:18:29,490 --> 00:18:30,990
and recondensation.

461
00:18:30,990 --> 00:18:33,640
And then, you can calculate this
from your chromatogram data.

462
00:18:33,640 --> 00:18:36,630
So when you have that
chromatograph data

463
00:18:36,630 --> 00:18:39,790
that has the peaks on it,
you can use this equation.

464
00:18:39,790 --> 00:18:43,220
So n is the number of
theoretical plates.

465
00:18:43,220 --> 00:18:46,610
This is just a
standard constant.

466
00:18:46,610 --> 00:18:50,250
And then your tr is
the retention time.

467
00:18:50,250 --> 00:18:54,892
So you'll use the retention
time of your peak in some unit.

468
00:18:54,892 --> 00:18:56,850
And then you want to take
the width of the peak

469
00:18:56,850 --> 00:19:00,770
at 1/2 of the
height of the peak.

470
00:19:00,770 --> 00:19:02,180
So I can't go backwards.

471
00:19:02,180 --> 00:19:03,630
Oh, there it is.

472
00:19:03,630 --> 00:19:07,430
So for this peak, you would say
your retention time is 1.434.

473
00:19:07,430 --> 00:19:10,393
And then, you would want
to go halfway up the peak,

474
00:19:10,393 --> 00:19:12,560
and then take the width of
that peak, which is going

475
00:19:12,560 --> 00:19:13,700
to be a very small number.

476
00:19:13,700 --> 00:19:16,580
And the best way to do this
is to probably use a ruler,

477
00:19:16,580 --> 00:19:18,230
and actually
measure, physically,

478
00:19:18,230 --> 00:19:20,570
the height of the peak,
and then measure the width

479
00:19:20,570 --> 00:19:22,410
at the halfway point.

480
00:19:22,410 --> 00:19:25,280
So if you do that, you
need to make sure that when

481
00:19:25,280 --> 00:19:27,350
you are using
these measurements,

482
00:19:27,350 --> 00:19:28,850
that they are in the same units.

483
00:19:28,850 --> 00:19:30,350
So you can either
do it in the units

484
00:19:30,350 --> 00:19:32,930
of time, which is what it's
given to you on the GC.

485
00:19:32,930 --> 00:19:34,580
But it's probably
a little easier

486
00:19:34,580 --> 00:19:36,588
if you do it in
millimeters or centimeters,

487
00:19:36,588 --> 00:19:37,880
however you want to measure it.

488
00:19:37,880 --> 00:19:40,550
Just make sure that
you also-- if you're

489
00:19:40,550 --> 00:19:43,580
going to measure your width
in centimeters or millimeters

490
00:19:43,580 --> 00:19:46,670
that you also measure your
retention time in centimeters

491
00:19:46,670 --> 00:19:47,385
or millimeters.

492
00:19:47,385 --> 00:19:49,010
And the retention
time is just the time

493
00:19:49,010 --> 00:19:52,460
from the beginning to
where your peak is.

494
00:19:57,480 --> 00:20:00,240
So that's GC spectroscopy.

495
00:20:00,240 --> 00:20:04,840
And now, we can talk a little
bit about IR spectroscopy.

496
00:20:04,840 --> 00:20:07,710
And if we take a
moment and think

497
00:20:07,710 --> 00:20:13,550
about our
electromagnetic spectrum,

498
00:20:13,550 --> 00:20:15,880
we can think about the
different types of energy

499
00:20:15,880 --> 00:20:18,440
that you have available in
the electromagnetic spectrum.

500
00:20:18,440 --> 00:20:21,110
So if this is our
wavelength in meters,

501
00:20:21,110 --> 00:20:23,420
what is our thing with the
smallest wavelength, highest

502
00:20:23,420 --> 00:20:23,920
energy?

503
00:20:26,350 --> 00:20:28,640
Anyone?

504
00:20:28,640 --> 00:20:29,360
Gamma rays.

505
00:20:32,780 --> 00:20:33,280
Then?

506
00:20:36,280 --> 00:20:38,935
AUDIENCE: X-rays?

507
00:20:38,935 --> 00:20:41,400
SARAH HEWETT: Then?

508
00:20:41,400 --> 00:20:42,487
UV.

509
00:20:42,487 --> 00:20:43,320
The little tiny one?

510
00:20:43,320 --> 00:20:44,010
AUDIENCE: Visible.

511
00:20:44,010 --> 00:20:44,927
SARAH HEWETT: Visible.

512
00:20:44,927 --> 00:20:46,170
AUDIENCE: And then infrared.

513
00:20:46,170 --> 00:20:47,128
SARAH HEWETT: Infrared.

514
00:20:47,128 --> 00:20:48,210
AUDIENCE: Microwave.

515
00:20:48,210 --> 00:20:54,090
SARAH HEWETT: And then,
yeah, microwave and radio.

516
00:20:57,740 --> 00:21:00,350
All right, so from highest
energy to lowest energy,

517
00:21:00,350 --> 00:21:02,260
this is our
electromagnetic spectrum.

518
00:21:02,260 --> 00:21:05,930
And so IR spectroscopy
uses IR radiation

519
00:21:05,930 --> 00:21:09,250
to give us information
about a molecule.

520
00:21:09,250 --> 00:21:11,000
And the way that this
happens is that it's

521
00:21:11,000 --> 00:21:12,875
very useful for identifying
functional groups

522
00:21:12,875 --> 00:21:13,640
in a molecule.

523
00:21:13,640 --> 00:21:17,090
And you pass this IR radiation
through the molecule.

524
00:21:17,090 --> 00:21:20,360
And all of the bonds
in your molecule

525
00:21:20,360 --> 00:21:23,090
have some sort of vibrational
energy associated with them.

526
00:21:23,090 --> 00:21:26,570
They're vibrating at
a certain frequency

527
00:21:26,570 --> 00:21:30,290
which corresponds to energy in
the IR region of the spectrum.

528
00:21:30,290 --> 00:21:34,190
So if you pass IR radiation
through your sample,

529
00:21:34,190 --> 00:21:37,300
then some of the
wavelengths will match up

530
00:21:37,300 --> 00:21:40,570
with the frequencies of the
vibrations of your bonds.

531
00:21:40,570 --> 00:21:43,138
And it will get absorbed.

532
00:21:43,138 --> 00:21:45,430
And then, you can measure
how much light comes back out

533
00:21:45,430 --> 00:21:46,570
and how much light
gets absorbed.

534
00:21:46,570 --> 00:21:48,670
And you can get an IR spectrum
of your molecule, which

535
00:21:48,670 --> 00:21:51,128
is representative of all the
different bonds and the energy

536
00:21:51,128 --> 00:21:52,470
that they absorb.

537
00:21:52,470 --> 00:21:57,120
The frequency of light or
energy that a bond absorbs

538
00:21:57,120 --> 00:22:00,180
is dependent on the
mass of the two atoms

539
00:22:00,180 --> 00:22:02,970
that are attached in the
bond, the bond strength,

540
00:22:02,970 --> 00:22:04,290
and the chemical environment.

541
00:22:04,290 --> 00:22:06,570
And this is related
by Hooke's law,

542
00:22:06,570 --> 00:22:09,238
if you're familiar with
physics, that talks about-- you

543
00:22:09,238 --> 00:22:11,280
can think about it as two
masses on opposite ends

544
00:22:11,280 --> 00:22:13,320
of the string-- or a spring.

545
00:22:13,320 --> 00:22:16,430
And so how much force you
need, or what the frequency is

546
00:22:16,430 --> 00:22:18,750
that that spring
will oscillate on

547
00:22:18,750 --> 00:22:21,050
depends on all of these factors.

548
00:22:21,050 --> 00:22:23,100
And so if you have something
that has a high bond

549
00:22:23,100 --> 00:22:26,812
order, like a double bond or
a triple bond, then those--

550
00:22:26,812 --> 00:22:28,020
that's a really tight spring.

551
00:22:28,020 --> 00:22:30,030
So it's going to vibrate
at a very high frequency,

552
00:22:30,030 --> 00:22:31,988
and it's going to take
a lot more energy to get

553
00:22:31,988 --> 00:22:33,570
that vibration to happen.

554
00:22:33,570 --> 00:22:35,340
Whereas if there are
two light atoms that

555
00:22:35,340 --> 00:22:37,007
are attached by a
single bond, then they

556
00:22:37,007 --> 00:22:41,080
will vibrate at a much lower
frequency-- less energy.

557
00:22:41,080 --> 00:22:44,160
Make sense, sort of?

558
00:22:44,160 --> 00:22:46,140
So vibrations are only
IR active if they change

559
00:22:46,140 --> 00:22:47,330
the dipole moment of a bond.

560
00:22:47,330 --> 00:22:50,050
So you can't see all the bonds
in your molecule using IR

561
00:22:50,050 --> 00:22:50,820
spectroscopy.

562
00:22:50,820 --> 00:22:52,860
You'll be able to see the ones--

563
00:22:52,860 --> 00:22:56,340
we can see most of them,
since most molecules are not

564
00:22:56,340 --> 00:22:57,450
perfectly symmetric.

565
00:22:57,450 --> 00:22:59,610
But like carbon-carbon
bonds, that stretch

566
00:22:59,610 --> 00:23:01,950
does not really change
the dipole much.

567
00:23:01,950 --> 00:23:04,180
So you don't see those
very strongly, if at all,

568
00:23:04,180 --> 00:23:05,490
in most of your IR spectra.

569
00:23:09,070 --> 00:23:10,960
So there are a bunch
of different ways

570
00:23:10,960 --> 00:23:14,650
that a bond or a
molecule can vibrate.

571
00:23:14,650 --> 00:23:18,340
And the number of possible
vibrational modes in a molecule

572
00:23:18,340 --> 00:23:20,720
is determined from the
degrees of freedom.

573
00:23:20,720 --> 00:23:23,590
So if you think
about a molecule,

574
00:23:23,590 --> 00:23:27,790
it can move in the
three dimensions

575
00:23:27,790 --> 00:23:30,258
of space translationally.

576
00:23:30,258 --> 00:23:32,800
And so all of the atoms can also
move in the three dimensions

577
00:23:32,800 --> 00:23:33,300
of space.

578
00:23:33,300 --> 00:23:36,410
So you get-- you start
with 3N degrees of freedom,

579
00:23:36,410 --> 00:23:39,580
so N being the number of
atoms in your molecule.

580
00:23:39,580 --> 00:23:42,310
And then in a linear
molecule, you have--

581
00:23:45,050 --> 00:23:46,690
you can also have
rotationally modes.

582
00:23:46,690 --> 00:23:48,065
But one of the
rotationally modes

583
00:23:48,065 --> 00:23:51,225
does not quite work as
well, because it's along

584
00:23:51,225 --> 00:23:52,100
the axis of the bond.

585
00:23:52,100 --> 00:23:54,517
So you're not changing anything
if you rotate it that way.

586
00:23:54,517 --> 00:23:57,433
So we end up with 3N
minus 5 vibrational

587
00:23:57,433 --> 00:23:58,600
stretching or bending modes.

588
00:23:58,600 --> 00:24:01,150
And then, in a
nonlinear molecule,

589
00:24:01,150 --> 00:24:05,540
you get all three translational
and all three rotational modes.

590
00:24:05,540 --> 00:24:07,210
So you do 3N minus 6.

591
00:24:07,210 --> 00:24:10,900
And so that gets rid of the
translational and rotational

592
00:24:10,900 --> 00:24:12,255
motion.

593
00:24:12,255 --> 00:24:13,630
So what's left is
the vibrational

594
00:24:13,630 --> 00:24:17,180
stretching or bending
modes in your molecule.

595
00:24:17,180 --> 00:24:19,270
And so the possible
vibrations that we

596
00:24:19,270 --> 00:24:23,130
can have are as follows--

597
00:24:23,130 --> 00:24:25,463
the symmetric stretch, the
asymmetric stretch, the bend,

598
00:24:25,463 --> 00:24:26,797
the wag, the twist, and rocking.

599
00:24:26,797 --> 00:24:28,250
So I need everybody to stand up.

600
00:24:28,250 --> 00:24:30,570
If you've done this before,
we're doing it again.

601
00:24:30,570 --> 00:24:33,120
This is a rite of passage
in a chemistry lab.

602
00:24:33,120 --> 00:24:36,080
We are going to--

603
00:24:36,080 --> 00:24:38,090
I will wait.

604
00:24:38,090 --> 00:24:41,330
We are going to pretend
that we are molecules,

605
00:24:41,330 --> 00:24:45,318
and we are going to act out all
of these different vibrations

606
00:24:45,318 --> 00:24:47,360
that can happen in your
molecule so that you have

607
00:24:47,360 --> 00:24:50,660
an idea of what you are looking
for when you see your IR

608
00:24:50,660 --> 00:24:51,330
spectrum.

609
00:24:51,330 --> 00:24:57,322
So if your body is like a
carbon, and then the rest of,

610
00:24:57,322 --> 00:24:59,030
like, your legs are
another carbon chain,

611
00:24:59,030 --> 00:25:01,890
then say you have two
hydrogen atoms in your hands.

612
00:25:01,890 --> 00:25:02,670
Great.

613
00:25:02,670 --> 00:25:04,790
We are excellent
methylene groups.

614
00:25:04,790 --> 00:25:06,260
So a symmetric stretch--

615
00:25:06,260 --> 00:25:07,640
any ideas?

616
00:25:07,640 --> 00:25:11,060
Yeah, when they go
at the same time.

617
00:25:11,060 --> 00:25:12,530
Excellent.

618
00:25:12,530 --> 00:25:14,420
The asymmetric stretch?

619
00:25:14,420 --> 00:25:17,750
Yeah, opposite, excellent.

620
00:25:17,750 --> 00:25:21,375
The bend or scissor?

621
00:25:21,375 --> 00:25:21,875
Excellent.

622
00:25:21,875 --> 00:25:23,458
So you're all getting
a workout today.

623
00:25:23,458 --> 00:25:24,650
This is great.

624
00:25:24,650 --> 00:25:26,570
The wag?

625
00:25:26,570 --> 00:25:28,960
The wag is back
and forth, like--

626
00:25:28,960 --> 00:25:30,240
yeah, there you go.

627
00:25:30,240 --> 00:25:31,700
Excellent.

628
00:25:31,700 --> 00:25:33,770
Twisting?

629
00:25:33,770 --> 00:25:35,270
One goes back, one goes forward.

630
00:25:35,270 --> 00:25:37,140
There we go.

631
00:25:37,140 --> 00:25:39,005
And then last one, rocking?

632
00:25:39,005 --> 00:25:40,130
That's what you had before.

633
00:25:40,130 --> 00:25:44,330
They're going back and
forth at the same time.

634
00:25:44,330 --> 00:25:45,110
Excellent!

635
00:25:45,110 --> 00:25:47,302
Well done.

636
00:25:47,302 --> 00:25:48,260
Give yourselves a hand.

637
00:25:53,930 --> 00:25:56,750
It's a good way to get
everybody up and moving.

638
00:26:02,680 --> 00:26:05,160
So those are our IR
vibrational modes,

639
00:26:05,160 --> 00:26:08,640
and those are all the ways that
you can make your molecules

640
00:26:08,640 --> 00:26:10,320
vibrate.

641
00:26:10,320 --> 00:26:12,130
And so now, how do
we measure this?

642
00:26:12,130 --> 00:26:15,130
And this is the
ATR spectrometer.

643
00:26:15,130 --> 00:26:16,380
It's an infrared spectrometer.

644
00:26:16,380 --> 00:26:18,047
This is the one that
we have in the lab.

645
00:26:18,047 --> 00:26:21,438
And it's in the very back
corner by the door in A prime 4.

646
00:26:21,438 --> 00:26:22,980
So some of you guys
may have seen it.

647
00:26:22,980 --> 00:26:25,470
You may have seen some of the
other lab groups coming in

648
00:26:25,470 --> 00:26:26,610
to use it.

649
00:26:26,610 --> 00:26:28,440
And the way that
this works is, it's

650
00:26:28,440 --> 00:26:31,230
a pretty simple instrument
in terms of what

651
00:26:31,230 --> 00:26:32,670
you need to do to use it.

652
00:26:32,670 --> 00:26:34,560
There is a crystal right here.

653
00:26:34,560 --> 00:26:37,170
And the crystals are usually
made of zinc selenide,

654
00:26:37,170 --> 00:26:40,470
or I believe, in our
case, it's a diamond.

655
00:26:40,470 --> 00:26:42,360
And it's a pretty tiny crystal.

656
00:26:42,360 --> 00:26:44,830
It's just that very, very
small little dot in the center.

657
00:26:44,830 --> 00:26:47,600
And you can take your
compound and put it

658
00:26:47,600 --> 00:26:48,600
straight on the crystal.

659
00:26:48,600 --> 00:26:51,660
And if it's a
solid, then you can

660
00:26:51,660 --> 00:26:54,373
use-- this is a
little pressure thing.

661
00:26:54,373 --> 00:26:56,790
So you can lower that, and
it'll press your solid right up

662
00:26:56,790 --> 00:26:58,740
against the crystal so
you get good contact.

663
00:26:58,740 --> 00:27:00,630
Or you can just put a couple
of drops of your liquid right

664
00:27:00,630 --> 00:27:02,755
on the crystal, and then
it has good contact anyway

665
00:27:02,755 --> 00:27:05,330
because it's a liquid.

666
00:27:05,330 --> 00:27:11,705
And-- oh, so the ATR stands for
attenuated total reflectance.

667
00:27:25,070 --> 00:27:29,630
And how it works is you have
a source of your IR energy.

668
00:27:29,630 --> 00:27:32,653
And these are some mirrors.

669
00:27:32,653 --> 00:27:33,820
And so you have your energy.

670
00:27:33,820 --> 00:27:34,490
It comes in here.

671
00:27:34,490 --> 00:27:35,930
It hits the mirror, and
then it gets directed up

672
00:27:35,930 --> 00:27:37,040
through this crystal.

673
00:27:37,040 --> 00:27:39,950
And like I said, you're
going to put your sample

674
00:27:39,950 --> 00:27:40,910
on top of the crystal.

675
00:27:44,400 --> 00:27:48,450
And you want to get really
good contact, because the IR

676
00:27:48,450 --> 00:27:51,510
energy will travel
through the crystal,

677
00:27:51,510 --> 00:27:54,120
and it'll interact with the
very bottom layer of your sample

678
00:27:54,120 --> 00:27:54,620
there.

679
00:27:57,003 --> 00:27:58,670
And then, it'll get
reflected back down.

680
00:27:58,670 --> 00:28:00,635
And in some cases, there's
only one reflection,

681
00:28:00,635 --> 00:28:02,010
and then it goes
to the detector.

682
00:28:02,010 --> 00:28:04,427
And in other cases, depending
on the size of your crystal,

683
00:28:04,427 --> 00:28:06,083
you can get multiple
reflections.

684
00:28:09,260 --> 00:28:12,000
And when the light interacts
with your sample, like I said,

685
00:28:12,000 --> 00:28:17,010
it'll absorb some of the
wavelengths of the IR light.

686
00:28:17,010 --> 00:28:18,680
So some of this
will get absorbed.

687
00:28:18,680 --> 00:28:21,740
And then, that's
the attenuation part

688
00:28:21,740 --> 00:28:24,180
is that some wavelengths
will be decreased

689
00:28:24,180 --> 00:28:27,470
in intensity because they'll
be absorbed by your compound.

690
00:28:27,470 --> 00:28:29,482
And then, the reflectance
part is the light

691
00:28:29,482 --> 00:28:31,940
gets reflected down through
this crystal into the detector.

692
00:28:31,940 --> 00:28:33,680
And then the detector
can determine

693
00:28:33,680 --> 00:28:36,050
which wavelengths of light
were absorbed and how much.

694
00:28:38,820 --> 00:28:42,210
And that is IR in a
very simplified fashion.

695
00:28:42,210 --> 00:28:46,063
There's more descriptions
of it in your Mohrig book.

696
00:28:46,063 --> 00:28:48,480
So if you guys have this book
or if you want to borrow it,

697
00:28:48,480 --> 00:28:50,460
there's an excellent
description of how different

698
00:28:50,460 --> 00:28:51,377
IR spectrometers work.

699
00:28:51,377 --> 00:28:54,000
There are a couple of different
ways to get IR samples.

700
00:28:54,000 --> 00:28:57,240
So like ATR is great
for liquids and solids.

701
00:28:57,240 --> 00:28:59,760
You can also have IR
spectrometers that just--

702
00:28:59,760 --> 00:29:02,850
you set your sample up on
some sort of support that's,

703
00:29:02,850 --> 00:29:03,870
like, vertical.

704
00:29:03,870 --> 00:29:05,850
And then you pass the
beam straight through it,

705
00:29:05,850 --> 00:29:07,892
and you measure what comes
out on the other side,

706
00:29:07,892 --> 00:29:09,600
kind of like the
UV-Vis that you did.

707
00:29:09,600 --> 00:29:11,970
So there's a couple
different ways to do IR.

708
00:29:11,970 --> 00:29:16,877
But this is the way that we're
going to be using in the lab.

709
00:29:16,877 --> 00:29:18,710
And what you get out
of it is an IR spectrum

710
00:29:18,710 --> 00:29:20,640
that looks something like this.

711
00:29:20,640 --> 00:29:22,520
So I took these straight
from the lab manual.

712
00:29:22,520 --> 00:29:26,210
And these are IR
spectra of carvone.

713
00:29:26,210 --> 00:29:28,550
And that's the carvone
from the caraway seed oil,

714
00:29:28,550 --> 00:29:30,550
and that's the carvone
from your peppermint oil.

715
00:29:30,550 --> 00:29:32,522
And do we see any differences?

716
00:29:37,610 --> 00:29:39,620
Not really.

717
00:29:39,620 --> 00:29:42,395
So what do we know is
different about the carvone

718
00:29:42,395 --> 00:29:44,270
from the caraway seed
and the peppermint oil?

719
00:29:48,070 --> 00:29:49,000
The stereochemistry.

720
00:29:49,000 --> 00:29:51,740
So we know that one is the
R form of the molecule,

721
00:29:51,740 --> 00:29:54,550
and the other is the
S. So this is the S

722
00:29:54,550 --> 00:29:56,290
and this is the R.
So is IR spectroscopy

723
00:29:56,290 --> 00:29:58,940
good at differentiating
between isomers?

724
00:29:58,940 --> 00:29:59,980
Nope, not at all.

725
00:29:59,980 --> 00:30:01,480
It just tells you what
functional groups are there.

726
00:30:01,480 --> 00:30:03,310
It doesn't really tell you
in what order they are in.

727
00:30:03,310 --> 00:30:05,643
So you'll need to do a different
spectroscopic technique

728
00:30:05,643 --> 00:30:07,220
if you want to figure that out.

729
00:30:07,220 --> 00:30:08,680
But we can get a
lot of information

730
00:30:08,680 --> 00:30:11,980
about different bonds that
are in our molecule, which

731
00:30:11,980 --> 00:30:16,320
is helpful for identifying
different things.

732
00:30:16,320 --> 00:30:17,857
What do we have next?

733
00:30:17,857 --> 00:30:20,190
So, yeah, we can talk about
interpreting an IR spectrum.

734
00:30:20,190 --> 00:30:23,070
So in your book
or on the internet

735
00:30:23,070 --> 00:30:25,440
there are many, many
charts that have

736
00:30:25,440 --> 00:30:27,895
lists and lists of the IR--

737
00:30:27,895 --> 00:30:29,460
oh, my bookmark fell out.

738
00:30:29,460 --> 00:30:30,430
Oh here it is.

739
00:30:30,430 --> 00:30:32,220
So there is a chart
in the Mohrig book

740
00:30:32,220 --> 00:30:35,430
that has a list of all of
the different stretching

741
00:30:35,430 --> 00:30:37,650
frequencies for different
functional groups.

742
00:30:37,650 --> 00:30:39,360
And it has the
stretching, the bending,

743
00:30:39,360 --> 00:30:41,580
and anything that
you are typically

744
00:30:41,580 --> 00:30:42,875
able to see in an IR spectrum.

745
00:30:42,875 --> 00:30:44,250
And it tells you
where you should

746
00:30:44,250 --> 00:30:48,520
look for it in the spectrum
in terms of wave numbers.

747
00:30:48,520 --> 00:30:52,470
So if you look at the
axes of these things,

748
00:30:52,470 --> 00:30:56,830
the left axis here is
percent transmittance,

749
00:30:56,830 --> 00:30:59,340
so how much of the
light gets through.

750
00:30:59,340 --> 00:31:02,390
And then, the--
so the top is 100.

751
00:31:02,390 --> 00:31:05,310
So if nothing is absorbed,
it'll be a baseline at the top.

752
00:31:05,310 --> 00:31:07,110
And then if things
are absorbed strongly,

753
00:31:07,110 --> 00:31:10,320
then the transmittance goes
down and you get a big peak.

754
00:31:10,320 --> 00:31:13,740
And then the wave, the other
axis along the bottom here,

755
00:31:13,740 --> 00:31:14,310
is--

756
00:31:14,310 --> 00:31:16,518
well, on the bottom of this
one, it's in micrometers.

757
00:31:16,518 --> 00:31:20,972
But in most cases in IR
now, we use wave numbers

758
00:31:20,972 --> 00:31:22,680
because it's a linear
measurement instead

759
00:31:22,680 --> 00:31:24,362
of non-linear.

760
00:31:24,362 --> 00:31:26,070
So wave numbers
corresponds to the amount

761
00:31:26,070 --> 00:31:29,880
of energy in the molecule--
or in the photon.

762
00:31:29,880 --> 00:31:32,173
So we can get these
charts of where

763
00:31:32,173 --> 00:31:33,590
different functional
groups absorb

764
00:31:33,590 --> 00:31:34,632
in terms of wave numbers.

765
00:31:34,632 --> 00:31:36,960
So these are all
in wave numbers,

766
00:31:36,960 --> 00:31:42,060
which is inverse centimeters.

767
00:31:42,060 --> 00:31:43,910
So when you get your
IR spectrum back

768
00:31:43,910 --> 00:31:45,770
and you take it in the lab,
you're going to print it out.

769
00:31:45,770 --> 00:31:48,020
And then, you can use one
of these charts to help you.

770
00:31:48,020 --> 00:31:50,420
And the best place to start
looking at an IR spectrum

771
00:31:50,420 --> 00:31:58,753
is between 4,000 and 1,400 wave
numbers, so, like, this half.

772
00:31:58,753 --> 00:32:00,170
Because you can
see, on this side,

773
00:32:00,170 --> 00:32:01,650
there's a lot
going on down here.

774
00:32:01,650 --> 00:32:04,350
And you might say, oh, that's
got a ton of information in it.

775
00:32:04,350 --> 00:32:05,012
Not so much.

776
00:32:05,012 --> 00:32:06,720
So this is called the
fingerprint region.

777
00:32:06,720 --> 00:32:08,090
And it does have a lot
of information in it.

778
00:32:08,090 --> 00:32:10,298
And before there were other
spectroscopic techniques,

779
00:32:10,298 --> 00:32:13,160
people spent a lot of time
trying to identify peaks down

780
00:32:13,160 --> 00:32:14,720
here.

781
00:32:14,720 --> 00:32:18,890
But they're less representative
of actual specific bonds.

782
00:32:18,890 --> 00:32:22,610
A lot of it's, like, overtones
and other resonance happening.

783
00:32:22,610 --> 00:32:25,670
And these are unique
to every chemical.

784
00:32:25,670 --> 00:32:27,230
So if you have a
reference spectrum

785
00:32:27,230 --> 00:32:28,910
and then you have your
spectrum, you can match them up

786
00:32:28,910 --> 00:32:31,130
and the fingerprint region
should match really well.

787
00:32:31,130 --> 00:32:33,230
But it's kind of
hard to interpret,

788
00:32:33,230 --> 00:32:34,430
and it's usually very messy.

789
00:32:34,430 --> 00:32:36,860
So we kind of ignore
this at the beginning.

790
00:32:36,860 --> 00:32:38,895
And then, if you look
over here, then there's

791
00:32:38,895 --> 00:32:40,520
a lot fewer peaks to
deal with and they

792
00:32:40,520 --> 00:32:44,390
provide a lot of information.

793
00:32:44,390 --> 00:32:48,220
So you'll see that the C-H
stretches are typically around,

794
00:32:48,220 --> 00:32:51,490
like, 2,800 to
3,100 wave numbers.

795
00:32:51,490 --> 00:32:54,130
And it depends on whether
it's a single bond

796
00:32:54,130 --> 00:32:57,637
like an alkane C-H, or
alkene, or an aromatic where

797
00:32:57,637 --> 00:32:58,220
they come out.

798
00:32:58,220 --> 00:33:03,100
So these guys, you'll
have different peaks,

799
00:33:03,100 --> 00:33:06,370
because we have some alkene
C-H's and some alkane C-H's.

800
00:33:06,370 --> 00:33:11,297
So you'll have a whole variety
of C-H stretching there.

801
00:33:11,297 --> 00:33:12,880
And then, what other
functional groups

802
00:33:12,880 --> 00:33:14,560
do we have in the molecule?

803
00:33:14,560 --> 00:33:15,710
What's the other main one?

804
00:33:15,710 --> 00:33:16,390
AUDIENCE: CO.

805
00:33:16,390 --> 00:33:17,265
SARAH HEWETT: The CO.

806
00:33:17,265 --> 00:33:20,650
And the CO double bond is one
of the most characteristic peaks

807
00:33:20,650 --> 00:33:22,150
that you can find
in an IR spectrum.

808
00:33:22,150 --> 00:33:25,030
And it always comes out
somewhere between 1600, 1700.

809
00:33:25,030 --> 00:33:27,110
So you can see, at 1700,
there is this huge peak.

810
00:33:27,110 --> 00:33:28,735
It is the biggest
peak in the spectrum.

811
00:33:28,735 --> 00:33:30,887
And that corresponds to
that CO double bond there.

812
00:33:30,887 --> 00:33:32,470
So that's always a
good place to start

813
00:33:32,470 --> 00:33:34,762
if you are looking to identify
something that you think

814
00:33:34,762 --> 00:33:35,990
may have a carbonyl in it.

815
00:33:35,990 --> 00:33:36,490
Yes?

816
00:33:36,490 --> 00:33:39,679
AUDIENCE: So can you tell how
many C-c bonds there are based

817
00:33:39,679 --> 00:33:41,420
on the height of the peak?

818
00:33:41,420 --> 00:33:43,100
SARAH HEWETT: No.

819
00:33:43,100 --> 00:33:45,500
So the height of the
peak doesn't give you

820
00:33:45,500 --> 00:33:48,080
any specific information
like how many there are.

821
00:33:48,080 --> 00:33:52,070
In amines, if you have a primary
versus a secondary amine--

822
00:33:52,070 --> 00:33:55,910
so if you have an
amine with 1 H on it,

823
00:33:55,910 --> 00:34:00,920
and some other R group
versus two H's, you'll

824
00:34:00,920 --> 00:34:03,470
see either two peaks and
the amine or one peak.

825
00:34:03,470 --> 00:34:06,410
So that's when you can
quantify atoms through this.

826
00:34:06,410 --> 00:34:11,650
But no, the intensity
does not always

827
00:34:11,650 --> 00:34:13,600
correspond to how
many of the bond

828
00:34:13,600 --> 00:34:17,018
there are, since the intensity
is mostly a function of how

829
00:34:17,018 --> 00:34:18,310
much the dipole moment changes.

830
00:34:18,310 --> 00:34:20,469
So you could have
a lot of C-H bonds,

831
00:34:20,469 --> 00:34:23,020
but you won't see a whole--

832
00:34:23,020 --> 00:34:25,370
like, a very intense peak.

833
00:34:25,370 --> 00:34:25,870
Yeah.

834
00:34:29,500 --> 00:34:30,909
Whoops!

835
00:34:30,909 --> 00:34:32,380
Go back.

836
00:34:32,380 --> 00:34:34,900
So things that you should do
is to look for what is there

837
00:34:34,900 --> 00:34:36,210
and look for what is not there.

838
00:34:36,210 --> 00:34:37,719
So if you know what's
supposed to be there

839
00:34:37,719 --> 00:34:38,725
in your functional
groups because you know

840
00:34:38,725 --> 00:34:39,969
the structure of your
molecule, then you

841
00:34:39,969 --> 00:34:41,920
can try to identify the
peaks that correspond

842
00:34:41,920 --> 00:34:43,460
to those functional groups.

843
00:34:43,460 --> 00:34:45,668
So if you are anticipating
having an O-H stretch,

844
00:34:45,668 --> 00:34:47,710
like you've made an alcohol
or a carboxylic acid,

845
00:34:47,710 --> 00:34:50,440
then you should see
a giant, broad peak

846
00:34:50,440 --> 00:34:53,965
around 3,500 wave numbers.

847
00:34:53,965 --> 00:34:56,340
And you should also, if you
are making a carboxylic acid,

848
00:34:56,340 --> 00:34:57,630
you should see this
O-H stretch, and you

849
00:34:57,630 --> 00:34:58,620
should see your carbonyl peak.

850
00:34:58,620 --> 00:35:00,037
So you need to be
able to identify

851
00:35:00,037 --> 00:35:01,412
all the peaks that
are associated

852
00:35:01,412 --> 00:35:02,770
with a certain functional group.

853
00:35:02,770 --> 00:35:05,187
So don't say that you have a
carboxylic acid if you cannot

854
00:35:05,187 --> 00:35:06,240
find either--

855
00:35:06,240 --> 00:35:08,470
if you cannot find
both of these peaks.

856
00:35:08,470 --> 00:35:10,310
They will be there.

857
00:35:10,310 --> 00:35:13,700
And then, less helpful
for us maybe now,

858
00:35:13,700 --> 00:35:16,883
but in the ester lab, which
we'll talk about later,

859
00:35:16,883 --> 00:35:18,550
you can also look for
what is not there.

860
00:35:18,550 --> 00:35:19,640
So if you're trying
to figure out

861
00:35:19,640 --> 00:35:21,170
if your synthesis
was successful,

862
00:35:21,170 --> 00:35:22,940
and you start with an
alcohol, and you're supposed

863
00:35:22,940 --> 00:35:25,148
to end with something that
does not have an O-H peak,

864
00:35:25,148 --> 00:35:27,350
then you can look for the
absence of an O-H stretch.

865
00:35:27,350 --> 00:35:28,940
Or if you're trying to
get rid of a carbonyl,

866
00:35:28,940 --> 00:35:30,315
then you can say
what's not there

867
00:35:30,315 --> 00:35:34,490
if you're trying to hydrogenate
some sort of double bond.

868
00:35:34,490 --> 00:35:36,840
You can figure out what is
there and what is not there.

869
00:35:36,840 --> 00:35:40,100
So those are things you can
talk about in your discussion.

870
00:35:40,100 --> 00:35:41,810
And your IR spectrum
in your report

871
00:35:41,810 --> 00:35:43,222
should be attached
as an appendix

872
00:35:43,222 --> 00:35:44,180
with key peaks labeled.

873
00:35:44,180 --> 00:35:45,770
So you can actually,
on your spectrum,

874
00:35:45,770 --> 00:35:49,220
write what each peak represents.

875
00:35:49,220 --> 00:35:51,260
So if you see a
giant peak at 1700,

876
00:35:51,260 --> 00:35:55,643
you can draw an arrow to it and
say, C double bond O stretch.

877
00:35:55,643 --> 00:35:57,060
And the way that
this is typically

878
00:35:57,060 --> 00:35:58,410
reported in the
literature-- and there's

879
00:35:58,410 --> 00:35:59,530
a bunch of different
ways to do it.

880
00:35:59,530 --> 00:36:01,988
You can check out the ACS style
guide for more information.

881
00:36:01,988 --> 00:36:04,115
But you'll say, IR spectroscopy.

882
00:36:04,115 --> 00:36:06,990
You use the type of IR
spectroscopy, which in our case

883
00:36:06,990 --> 00:36:07,878
is going to be ATR.

884
00:36:07,878 --> 00:36:10,170
So there is, like, thin film,
there's potassium bromide

885
00:36:10,170 --> 00:36:11,520
pellets, there's all
kinds of different ways

886
00:36:11,520 --> 00:36:13,140
that you can take
an IR spectrum.

887
00:36:13,140 --> 00:36:16,410
And the method that you use will
also affect the peak intensity.

888
00:36:16,410 --> 00:36:22,260
So that's why it's not as
helpful of a thing to look at.

889
00:36:22,260 --> 00:36:24,660
And then, your units,
wave numbers, and then

890
00:36:24,660 --> 00:36:28,660
your key peaks-- so if you have
a peak that is really broad,

891
00:36:28,660 --> 00:36:30,240
you only have to report.

892
00:36:30,240 --> 00:36:34,200
And you'll see that most of
the peaks in an IR spectrum

893
00:36:34,200 --> 00:36:35,730
are not super sharp.

894
00:36:35,730 --> 00:36:38,700
So this carbonyl peak,
if you look at the base,

895
00:36:38,700 --> 00:36:40,927
it ranges through a good
number of wave numbers.

896
00:36:40,927 --> 00:36:43,260
But when you report it, you
only report the wave numbers

897
00:36:43,260 --> 00:36:46,230
of the highest intensity.

898
00:36:46,230 --> 00:36:49,230
And the instrument will
print that out for you

899
00:36:49,230 --> 00:36:52,470
on your spectrum, so you'll
know what the highest

900
00:36:52,470 --> 00:36:56,010
intensity is for your peak.

901
00:36:56,010 --> 00:36:59,490
So you can report the highest
intensity wave numbers

902
00:36:59,490 --> 00:37:00,690
for each of your peaks.

903
00:37:00,690 --> 00:37:04,210
And if you know what the
peak is, in some cases,

904
00:37:04,210 --> 00:37:06,660
people will put what
bond it represents.

905
00:37:06,660 --> 00:37:09,180
You don't have to.

906
00:37:09,180 --> 00:37:10,745
It was acceptable
to do it both ways

907
00:37:10,745 --> 00:37:12,120
according to the
ACS style guide.

908
00:37:12,120 --> 00:37:14,750
So that's kind of up to you.

909
00:37:14,750 --> 00:37:18,118
A little more helpful for
the person reading it, but--

910
00:37:18,118 --> 00:37:19,910
So if we want to take
a look really quickly

911
00:37:19,910 --> 00:37:23,480
at a couple of IR spectra
of molecules that--

912
00:37:23,480 --> 00:37:24,650
well, this one you may know.

913
00:37:24,650 --> 00:37:26,340
So this is the IR
spectrum of ethanol.

914
00:37:26,340 --> 00:37:28,820
And what is the major feature
that we care about here?

915
00:37:32,490 --> 00:37:34,310
So there's the C--

916
00:37:34,310 --> 00:37:36,630
C-O, but the-- yeah, there's
the O-H. So the biggest,

917
00:37:36,630 --> 00:37:39,770
strongest feature
here is our O-H peak.

918
00:37:39,770 --> 00:37:42,080
And O-H peaks are
typically quite broad.

919
00:37:42,080 --> 00:37:44,330
So they're not as sharp and
defined as the other peaks

920
00:37:44,330 --> 00:37:44,820
in the spectrum.

921
00:37:44,820 --> 00:37:46,820
So that's one of the
characteristic ways you can

922
00:37:46,820 --> 00:37:49,722
know if you have an alcohol.

923
00:37:49,722 --> 00:37:50,680
And then, you can look.

924
00:37:50,680 --> 00:37:54,370
And we have some methyl
C-H's and ethyl C-H's here.

925
00:37:54,370 --> 00:37:56,650
So you have alkane C-H's.

926
00:37:56,650 --> 00:38:01,090
And so those show up a little
bit below 3,000 wave numbers.

927
00:38:01,090 --> 00:38:02,050
Great.

928
00:38:02,050 --> 00:38:04,150
And then, you may
be able to find

929
00:38:04,150 --> 00:38:06,790
the C-O bond that typically
shows up around 1,000,

930
00:38:06,790 --> 00:38:07,400
give or take.

931
00:38:07,400 --> 00:38:12,363
So maybe one of those peaks
is your C-O stretch as well.

932
00:38:12,363 --> 00:38:14,530
So sometimes you can go
into that fingerprint region

933
00:38:14,530 --> 00:38:15,880
if you know that there
is something there

934
00:38:15,880 --> 00:38:16,922
that you are looking for.

935
00:38:16,922 --> 00:38:19,615
So the C-O stretch is one
that you typically can see,

936
00:38:19,615 --> 00:38:20,990
and it's typically
pretty strong.

937
00:38:20,990 --> 00:38:23,380
So in this case, it is there.

938
00:38:23,380 --> 00:38:27,520
But, yeah, and then
another example

939
00:38:27,520 --> 00:38:31,390
is this compound, which
is 3, 7 dimethyl octonal.

940
00:38:31,390 --> 00:38:34,090
And what do we have here that's
really strong and sticking out?

941
00:38:38,490 --> 00:38:41,383
D double bond O, again, right
here around 1700 wave numbers,

942
00:38:41,383 --> 00:38:43,050
that's always a dead
giveaway that there

943
00:38:43,050 --> 00:38:44,850
is some sort of carbonyl peak.

944
00:38:44,850 --> 00:38:46,747
And if you have an
aldehyde peak, then--

945
00:38:46,747 --> 00:38:48,330
I didn't write it
up here-- but you'll

946
00:38:48,330 --> 00:38:51,990
have a characteristic stretch
for this aldehyde hydrogen that

947
00:38:51,990 --> 00:38:54,650
is also up here.

948
00:38:54,650 --> 00:38:58,100
And then you have a couple
of alkene C-H stretches,

949
00:38:58,100 --> 00:38:59,630
and a bunch of
alkane C-H stretches.

950
00:38:59,630 --> 00:39:01,730
So in this case, there
is a lot going on

951
00:39:01,730 --> 00:39:03,510
in our stretching region.

952
00:39:03,510 --> 00:39:06,730
And those are the major
features of that spectrum.

953
00:39:06,730 --> 00:39:08,803
So we'll go over this
a little bit more also,

954
00:39:08,803 --> 00:39:10,470
again, when we talk
about the ester lab.

955
00:39:10,470 --> 00:39:12,850
Because you're going to be
using IR for that lab as well.

956
00:39:12,850 --> 00:39:14,430
We can talk about some of the
different functional groups

957
00:39:14,430 --> 00:39:15,900
that you can see in
that case, because we're

958
00:39:15,900 --> 00:39:17,400
going to be dealing
with, obviously,

959
00:39:17,400 --> 00:39:21,500
esters, and some alcohols,
and some ketones,

960
00:39:21,500 --> 00:39:23,350
and some carboxylic acids.

961
00:39:23,350 --> 00:39:28,990
So that is a brief
overview of IR.

962
00:39:28,990 --> 00:39:31,120
So we have one more
technique left to talk about,

963
00:39:31,120 --> 00:39:33,790
and it is the polarimetry.

964
00:39:33,790 --> 00:39:37,210
And to talk about
that, first, we're

965
00:39:37,210 --> 00:39:40,150
going to do another round of
synthesis with your products

966
00:39:40,150 --> 00:39:42,322
that you've separated in
your initial distillation.

967
00:39:42,322 --> 00:39:43,780
So you have your
limonene fraction,

968
00:39:43,780 --> 00:39:45,363
your carvone fraction,
and we're going

969
00:39:45,363 --> 00:39:47,230
to take the carvone
fraction and synthesize

970
00:39:47,230 --> 00:39:51,430
a semi-carbazone, which will
look something like this.

971
00:39:51,430 --> 00:39:53,620
And you will make this molecule.

972
00:39:53,620 --> 00:39:55,170
It'll still have
your stereocenter.

973
00:39:55,170 --> 00:39:56,250
We're not touching that.

974
00:39:56,250 --> 00:39:59,130
So it'll keep your
RS configuration.

975
00:39:59,130 --> 00:40:01,158
And it'll be a solid, though.

976
00:40:01,158 --> 00:40:02,700
So you're going to
start with an oil.

977
00:40:02,700 --> 00:40:04,320
You will go through
this synthesis.

978
00:40:04,320 --> 00:40:06,612
And then you'll end up with
white needle-like crystals.

979
00:40:06,612 --> 00:40:09,930
So you're going to recrystallize
your product very, very slowly.

980
00:40:09,930 --> 00:40:11,740
And your TAs will show
you how to do that.

981
00:40:11,740 --> 00:40:13,573
There's a good procedure
in your lab manual,

982
00:40:13,573 --> 00:40:15,120
but you're going
to do the reaction,

983
00:40:15,120 --> 00:40:16,860
and then you're going to
let it sit in your lab bench

984
00:40:16,860 --> 00:40:19,237
until the next lab period,
so for a couple of days.

985
00:40:19,237 --> 00:40:21,570
And you want the crystals to
grow really, really slowly.

986
00:40:21,570 --> 00:40:24,870
So you will not see them
when you first make them,

987
00:40:24,870 --> 00:40:26,370
but you'll see them,
hopefully, when

988
00:40:26,370 --> 00:40:27,840
you come to lab the next time.

989
00:40:27,840 --> 00:40:29,850
And the slower the crystals
grow, the more pure they are.

990
00:40:29,850 --> 00:40:32,040
And then, we are going to
need very pure crystals,

991
00:40:32,040 --> 00:40:33,957
because these are what
you're going to analyze

992
00:40:33,957 --> 00:40:35,430
by X-ray crystallography.

993
00:40:35,430 --> 00:40:38,250
And like I said, Peter
Muller will come and give you

994
00:40:38,250 --> 00:40:39,610
more information on that.

995
00:40:39,610 --> 00:40:41,760
So stay tuned.

996
00:40:41,760 --> 00:40:43,650
But what we can do
with these crystals

997
00:40:43,650 --> 00:40:47,950
is use them to do
some polarimetry.

998
00:40:47,950 --> 00:40:52,020
So one of the things that
you'll know about your-- so

999
00:40:52,020 --> 00:40:55,980
I said you're going to
make some white crystals.

1000
00:40:55,980 --> 00:40:58,500
So one of the ways that we've
been analyzing our solids

1001
00:40:58,500 --> 00:40:59,790
is by melting point.

1002
00:40:59,790 --> 00:41:02,495
And you can get two
possible diastereomers out

1003
00:41:02,495 --> 00:41:03,245
of this synthesis.

1004
00:41:03,245 --> 00:41:04,995
So you can either
have-- since there's not

1005
00:41:04,995 --> 00:41:07,230
a lot of rotation around
the C-N double bond,

1006
00:41:07,230 --> 00:41:10,350
you either have that extra
nitrogen group pointing up

1007
00:41:10,350 --> 00:41:13,760
towards this methyl
group or away from it.

1008
00:41:13,760 --> 00:41:16,010
And these two compounds have
different melting points.

1009
00:41:16,010 --> 00:41:18,612
So you will characterize
your crystals

1010
00:41:18,612 --> 00:41:20,820
by melting point to figure
out which of these isomers

1011
00:41:20,820 --> 00:41:22,780
you have, the alpha or the beta.

1012
00:41:22,780 --> 00:41:25,020
Most people will make
the beta, because it

1013
00:41:25,020 --> 00:41:26,610
has less steric
hindrance, so it's

1014
00:41:26,610 --> 00:41:29,460
a little bit easier for that
to happen, just synthetically.

1015
00:41:29,460 --> 00:41:31,538
And so that's one
of the first ways

1016
00:41:31,538 --> 00:41:33,330
that you will characterize
these compounds.

1017
00:41:33,330 --> 00:41:35,910
And the second way
is by polarimetry.

1018
00:41:35,910 --> 00:41:43,770
And so if we talk
about polarized light

1019
00:41:43,770 --> 00:41:48,847
really fast, so what does it
mean for light to be polarized?

1020
00:41:52,050 --> 00:41:53,800
It's all going in
the same direction.

1021
00:41:53,800 --> 00:41:58,193
And so all-- so you have a light
source, and it emits light.

1022
00:41:58,193 --> 00:41:59,610
And all of the
waves are traveling

1023
00:41:59,610 --> 00:42:00,952
in all different directions.

1024
00:42:00,952 --> 00:42:02,910
But you can put it through
a polarizing filter,

1025
00:42:02,910 --> 00:42:05,030
and then you only filter
out the light that is--

1026
00:42:05,030 --> 00:42:08,490
that has, like, the molecules
are all arranged in slits

1027
00:42:08,490 --> 00:42:13,570
so that it only selects for
light traveling in one plane.

1028
00:42:13,570 --> 00:42:15,820
So you can put that there.

1029
00:42:15,820 --> 00:42:18,440
And if you-- if I have two
pieces of polarizing paper,

1030
00:42:18,440 --> 00:42:20,940
and I put them on top of each
other in the same orientation,

1031
00:42:20,940 --> 00:42:22,260
then the light pretty
much gets through.

1032
00:42:22,260 --> 00:42:24,302
These are a little bit
colored, so not all of it.

1033
00:42:24,302 --> 00:42:27,030
But then, if I rotate so that
the bottom one is selecting

1034
00:42:27,030 --> 00:42:30,360
for light going this way,
and the top one is selecting

1035
00:42:30,360 --> 00:42:31,860
for light going the
other direction,

1036
00:42:31,860 --> 00:42:36,450
then no light gets
through, because it

1037
00:42:36,450 --> 00:42:38,560
can't pass through the filter.

1038
00:42:38,560 --> 00:42:40,260
So that's what we're
going to-- this

1039
00:42:40,260 --> 00:42:43,110
is the essential principle
behind polarimetry.

1040
00:42:43,110 --> 00:42:47,100
So if you remember from either
your organic chemistry lectures

1041
00:42:47,100 --> 00:42:52,650
or experience before, different
molecules that are chiral

1042
00:42:52,650 --> 00:42:54,898
will rotate plane
polarized light.

1043
00:42:54,898 --> 00:42:56,940
And so what that means is
if you put a polarizing

1044
00:42:56,940 --> 00:42:59,370
filter on your light,
select for light all going

1045
00:42:59,370 --> 00:43:00,870
in one direction,
and then you shine

1046
00:43:00,870 --> 00:43:03,720
that light through
a chiral sample,

1047
00:43:03,720 --> 00:43:07,710
it'll get rotated to a
certain degree based on

1048
00:43:07,710 --> 00:43:10,260
a number of features,
but essentially,

1049
00:43:10,260 --> 00:43:12,820
how the light interacts
with your chiral sample.

1050
00:43:12,820 --> 00:43:16,530
And so if you have two
polarizing filters,

1051
00:43:16,530 --> 00:43:18,540
and you have your
sample in between them,

1052
00:43:18,540 --> 00:43:24,740
you can rotate one of
them, and eventually, it'll

1053
00:43:24,740 --> 00:43:27,510
match up again, and you'll see
all the light come through.

1054
00:43:27,510 --> 00:43:30,052
And so that's how you can tell
how much your compound rotates

1055
00:43:30,052 --> 00:43:30,552
the light.

1056
00:43:30,552 --> 00:43:32,420
So you put a polarizing
filter on each side,

1057
00:43:32,420 --> 00:43:35,365
and then kind of
rotate them until you

1058
00:43:35,365 --> 00:43:36,490
get all of your light back.

1059
00:43:36,490 --> 00:43:37,870
And then, you can
measure the polarimetry.

1060
00:43:37,870 --> 00:43:40,328
So that's kind of the way that
they did it in the old days,

1061
00:43:40,328 --> 00:43:43,570
but we have an instrument
that'll do it for you.

1062
00:43:43,570 --> 00:43:47,020
So you don't have to
worry about that too much.

1063
00:43:47,020 --> 00:43:48,520
I'll turn this back
on really quick.

1064
00:43:51,810 --> 00:43:53,940
But the rotation, like I
said, we can measure it.

1065
00:43:53,940 --> 00:43:55,420
And it's characteristic
of the molecules.

1066
00:43:55,420 --> 00:43:57,970
So the R and the S forms will
rotate in opposite directions.

1067
00:43:57,970 --> 00:43:59,640
So in our case,
the R form rotates

1068
00:43:59,640 --> 00:44:02,730
light in the negative
direction, or counterclockwise,

1069
00:44:02,730 --> 00:44:05,460
and then the S form
will rotate light

1070
00:44:05,460 --> 00:44:06,630
in the positive direction.

1071
00:44:06,630 --> 00:44:09,397
And the R and the S
are not really related

1072
00:44:09,397 --> 00:44:10,480
to the plus and the minus.

1073
00:44:10,480 --> 00:44:14,400
So for different compounds,
the R might be the plus isomer

1074
00:44:14,400 --> 00:44:15,780
and the S might be the minus.

1075
00:44:15,780 --> 00:44:17,447
It's something that
you have to measure.

1076
00:44:17,447 --> 00:44:20,520
You can't just know off
the top of your head.

1077
00:44:20,520 --> 00:44:23,070
And from this, we can
calculate the specific rotation

1078
00:44:23,070 --> 00:44:25,947
of our light, which is how
much the light has rotated.

1079
00:44:25,947 --> 00:44:28,530
And it depends on the length of
the sample, the concentration,

1080
00:44:28,530 --> 00:44:30,180
and the wavelengths
of light that is used,

1081
00:44:30,180 --> 00:44:31,300
and then, again,
the temperature,

1082
00:44:31,300 --> 00:44:33,342
because that impacts the
density of your solution

1083
00:44:33,342 --> 00:44:34,175
or of your compound.

1084
00:44:34,175 --> 00:44:36,259
So the way that you're
going to do this in the lab

1085
00:44:36,259 --> 00:44:38,730
is you're going to take a
sample of your crystals,

1086
00:44:38,730 --> 00:44:39,720
and then you're going
to weigh them out,

1087
00:44:39,720 --> 00:44:41,430
and you're going to
dissolve them in ethanol.

1088
00:44:41,430 --> 00:44:42,847
So you're going
to make a solution

1089
00:44:42,847 --> 00:44:44,700
that you know the
concentration of so

1090
00:44:44,700 --> 00:44:48,880
that we can plug that in
for our concentration.

1091
00:44:48,880 --> 00:44:51,715
And you will put
it in these tubes.

1092
00:44:51,715 --> 00:44:54,090
And then you will insert the
tube into the polar emitter,

1093
00:44:54,090 --> 00:44:55,110
and it will shine
the light through.

1094
00:44:55,110 --> 00:44:57,300
And then it will calculate
what the angle is

1095
00:44:57,300 --> 00:44:58,745
that the light gets rotated by.

1096
00:44:58,745 --> 00:45:00,120
And the polarimeter
actually will

1097
00:45:00,120 --> 00:45:03,150
calculate the specific rotation
for you, which is kind of nice.

1098
00:45:03,150 --> 00:45:05,205
But you can also calculate it.

1099
00:45:05,205 --> 00:45:07,580
It gives you all the information
to calculate it yourself

1100
00:45:07,580 --> 00:45:08,970
as well.

1101
00:45:08,970 --> 00:45:12,440
So this is notated
very similarly

1102
00:45:12,440 --> 00:45:16,040
to our refractive index,
in that it is taken

1103
00:45:16,040 --> 00:45:17,325
at 20 degrees for the density.

1104
00:45:17,325 --> 00:45:18,950
And we use the same
wavelength of light

1105
00:45:18,950 --> 00:45:21,560
from that sodium D-line,
the 586 nanometers,

1106
00:45:21,560 --> 00:45:23,730
in order to have a
consistent representation.

1107
00:45:23,730 --> 00:45:26,840
So you may see these
constants in the literature.

1108
00:45:26,840 --> 00:45:28,340
And if the temperature
is different,

1109
00:45:28,340 --> 00:45:30,830
it'll say something
like 23 or 25,

1110
00:45:30,830 --> 00:45:32,900
or whatever the temperature
they took it at.

1111
00:45:32,900 --> 00:45:35,570
And you can also change this to
whatever nanometer wavelength

1112
00:45:35,570 --> 00:45:36,845
of light that you used.

1113
00:45:36,845 --> 00:45:38,720
But we're going to be
using these conditions.

1114
00:45:38,720 --> 00:45:41,900
And then this is the rotation
of the light in degrees,

1115
00:45:41,900 --> 00:45:43,640
the length the travels
in decimeters--

1116
00:45:43,640 --> 00:45:45,473
so you're going to
measure the tube that you

1117
00:45:45,473 --> 00:45:47,810
use in decimeters-- and then
your concentration in grams

1118
00:45:47,810 --> 00:45:48,260
per milliliter.

1119
00:45:48,260 --> 00:45:50,052
And you can calculate
the specific rotation

1120
00:45:50,052 --> 00:45:53,670
of the molecules.

1121
00:45:53,670 --> 00:45:56,060
So hopefully, the people
who had different isomers

1122
00:45:56,060 --> 00:45:58,160
will rotate-- the light
will get rotated exactly

1123
00:45:58,160 --> 00:46:02,100
in the same number of degrees,
but in opposite directions

1124
00:46:02,100 --> 00:46:04,100
if we've done
everything correctly.

1125
00:46:04,100 --> 00:46:07,500
So you'll see what you
can get from there.

1126
00:46:07,500 --> 00:46:09,060
And I think that
is all for today.

1127
00:46:09,060 --> 00:46:11,090
Do you guys have any
questions about anything

1128
00:46:11,090 --> 00:46:13,132
that we are about to do
in the essential oil lab?

1129
00:46:13,132 --> 00:46:14,960
Autumn?

1130
00:46:14,960 --> 00:46:19,780
AUDIENCE: Why is-- in this
case, why is gas [INAUDIBLE]??

1131
00:46:19,780 --> 00:46:24,420
SARAH HEWETT: In this case,
to be perfectly honest,

1132
00:46:24,420 --> 00:46:26,760
I am not super
familiar with HPLC.

1133
00:46:26,760 --> 00:46:31,400
I'm sure you could also use it
to separate these compounds.

1134
00:46:31,400 --> 00:46:34,020
GC is-- I mean, part
of it is the techniques

1135
00:46:34,020 --> 00:46:35,650
that we have available to us.

1136
00:46:35,650 --> 00:46:36,690
So there's that.

1137
00:46:36,690 --> 00:46:38,580
But this also gets
separated really nicely

1138
00:46:38,580 --> 00:46:39,580
based on boiling point.

1139
00:46:39,580 --> 00:46:41,372
So it's kind of fast
and easy for us to do.

1140
00:46:41,372 --> 00:46:43,860
But I can also-- yeah, we
can talk about it more.

1141
00:46:43,860 --> 00:46:46,340
Yeah, no, it's a good question.