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[CLICKING]

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JOHN GRIMES: OK,
well, I guess I'll

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get started, and let
people trickle in,

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if anybody else is coming in.

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So my name is John Grimes.

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And I work in the chemistry
department's Instrumentation

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Facility.

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And down there,
we've got a number

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of different instruments.

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We have five mass
spec instruments.

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That is not my specialty.

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So other than being
able to point them out,

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I can't really tell you
that much about them.

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I help run NMRs.

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And so what I do is I teach
students how to use the NMRs.

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I will help them select what
experiments they possibly

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need to use in order to give
them the answer that they're

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looking for.

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And I'll also help them
interpret the data,

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or at least get them started
off on interpreting the data so

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that they can do
that on their own

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when they're doing
their own research.

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So what I hope to talk
to you about today

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is what an NMR instrument
is and what it actually

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consists of as far
as the parts, what

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the analytical
technique of NMR is,

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and how we measure
the signal, and then

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go into some examples of
how to interpret the data.

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So here's a picture of one
of our instruments there.

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And here's an example
spectrum of adenosine.

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So nuclear magnetic resonance
is what NMR stands for.

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And it's the study of
molecular structure

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by measuring the interaction
of radio frequency energy

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with a collection of
nuclei that you've taken

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and you've put into a
strong magnetic field.

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So it's an analytical technique
that is based on a nucleus's--

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or nuclei-- intrinsic
angular momentum.

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It is a nondestructive
analytical technique.

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And that's important if
you're a graduate student

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in the chemistry
department, wherever,

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even an undergraduate, and
you have worked long and hard

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to synthesize some
natural product that's

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15 steps into a
synthesis, you've only

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got a half milligram
of that, and it's

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a year's worth of
your life's work,

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you don't want to destroy
that sample analyzing it.

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So you can take
that sample, and you

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can put it in a small, little,
cylindrical glass tube.

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You can analyze it.

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And then you can take
that sample back out

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and use it for something else.

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So the technique allows you
to determine connectivity

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within a molecule.

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So I've drawn-- this
is something I'll

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bring up a spectrum of later.

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It's just three heptanone.

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But it will allow you to see
that protons on this terminal

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carbon are connected to that
and next to a carbon here

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that has two protons on it.

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So it looks through
bond connectivity.

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And it won't necessarily give
you connectivity all the way

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through the molecule, but
you can build up, say,

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this chunk of the
molecule and this chunk.

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And then you can
link it together--

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picture linking together a chain
that allows you to put together

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the whole molecule.

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It will also show you
interactions through space.

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I'm not going to embarrass
myself and try and draw

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a protein.

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But there can be two
parts of a molecule that

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are hundreds of atoms
away from each other

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if you were to try and go
through the chemical bonds.

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Yet they're held near
each other in space.

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And you can monitor
how close they are.

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And that helps determine the
three-dimensional structure

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of molecules.

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And so all the time protein
structures are solved by NMR.

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And you can use it to
monitor other processes too,

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such as whether a protein
has bound a small molecule,

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whether there's hindered
rotation about a bond,

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so something like--

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where did my chalk go?

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If you take something
like dimethylformamide,

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this bond here has partial
double bond character.

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And you can see separate
peaks for those methyl groups.

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And you can rationalize it
by the hindered rotation

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around that bond.

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And there even other techniques.

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And so everybody is going to
be familiar with what NMR is.

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And hopefully none of
you have had to have one,

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but it's the same physical
technique as an MRI.

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So here's an MRI
of, unfortunately,

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my daughter's head after
she swam into the pool

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end in a swim match.

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Nothing happened to her, but
you can take pictures with NMR.

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In the past, I've used it
to take pictures of insects.

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You can also do
analytical techniques

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of in vitro diagnostics.

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So there's a test out there
called the NMR LipoProfile.

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And it will analyze
your cholesterol, i.e.

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the density-- or the
concentration of lipoproteins

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that's circulating
around in your blood.

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So what is an NMR instrument?

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NMR instruments
come in two flavors.

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Or at least-- maybe they
come in more flavors,

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but, here at MIT, we have
two types of NMR instruments.

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There are ones that are
referred to as high-resolution

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instruments, which usually
have a stronger magnet,

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and they're bigger.

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There are also desk--

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they're not desktop, but
benchtop instruments,

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which is what you're
going to use in your lab.

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So each of these has the
exact same constituent parts.

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I didn't go over and try and
take your benchtop instrument

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apart to get a
picture of those parts

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because I wouldn't have
gotten it back together.

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And it would have never worked.

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So I'm going to go through
one of our instruments

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and show you the
individual parts,

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but keep in mind it's the
exact same thing that's

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in the instrument
that you'll be using.

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So you've got to have
a strong magnetic field

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to immerse your sample in.

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And obviously that's
supplied by a strong magnet.

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So magnets will
come in two flavors.

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In the benchtop instruments,
they are a permanent magnet.

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Has anybody ever taken
apart old computers,

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and you can get the
hard drives, and there

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are strong magnets in there
that are sort of silver colored?

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Those are made from a
neodymium-iron-boron alloy.

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And that is what they use for
the permanent magnets that

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are in the benchtop systems.

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There's been a great improvement
in those in the past, I guess,

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15 years or so.

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There used not to be any
benchtop instruments.

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It was difficult to
engineer and machine

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permanent magnets that would
give a uniform magnetic field.

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But they've been
able to do that.

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And so there are a lot
of benchtop instruments

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that are out there now.

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The standard NMR-- well, they're
termed high-resolution NMRs

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because they have stronger
magnetic fields that then can

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be generated from
permanent magnets--

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use what are called
superconducting magnets.

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So the magnetic
field is generated

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by the circulation of electric
charge in a superconductor.

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And, if you're familiar with
superconductors, usually,

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they have to be below
some specific temperature

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in order to maintain
their conductivity.

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While the temperature,
the critical temperature,

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has come up in recent
years for superconductors,

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as far as producing
something that's

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easily machinable into wire
that you can wrap into a coil,

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the higher temperature--
higher critical temperature

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superconductors aren't
easily malleable.

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So you still have
to use something

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that you've got to
get really cold, i.e.

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down to liquid
helium temperature.

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So, in a superconducting
magnet, you've got--

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think of it as a giant thermos,
which is what this can is.

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You've got a hole through
the center, which is called

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the room temperature bore.

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It's room temperature
because it is not cold.

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Your sample, which is
in this little tube

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that I showed you
generally, will

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be held in what's
called a spinner, so

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this little blue thing.

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You will put it in
the top of the magnet.

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And it will just ride
down on a cushion of air

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somewhere to about there
in the center of magnet--

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in the center of the magnet.

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On the benchtop
instrument, what's nice--

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let's see if I can
back up a slide.

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All you do-- you can
see it, and it'll

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be obvious when you run it
in the lab for yourself.

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You just put the tube
right down in there.

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You don't have to put it
in any specific holder.

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So your sample tube
goes down that bore.

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From underneath the
instrument comes

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the NMR probe, which I'll
talk about in a second.

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So that superconducting
wire is wound

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in a coil around that
room temperature bore.

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This chamber here, which,
if I could see, is number 6,

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that is a chamber that
is full of liquid helium.

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So, when you set up one of
these magnets, you cool it off.

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You fill that with
liquid helium.

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And then you put a charge on
this superconducting wire.

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And the charge is
about 100 to 200 amps.

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And 200 amps is the
amount of charge

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that goes through a
medium-sized house.

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So it's got a good amount
of electricity on there

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that's circulating around.

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As long as you keep it
cold, meaning as long

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as you top it off with liquid
helium every few months,

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it's going to remain a magnet
and generate a powerful field.

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So, if you just had liquid
helium touching metal,

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the outside of that metal
would be a big chunk of ice.

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So this has an evacuated--

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not layer, but I
guess a portion of it

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that's evacuated with a high
vacuum to provide insulation.

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Outside of that is a
layer of liquid nitrogen.

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And we fill that weekly.

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And that just cuts down on
any thermal transmission,

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even though you've got
a high vacuum there.

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And then outside of that is
another high vacuum layer

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and then the room.

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And so you can walk up to the
can, and you can touch it.

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And it won't feel cold at all.

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So that's what the
magnet consists of.

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The NMR measurement is based
on the strength of the magnet--

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so B0 is what I'm calling that--

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and the gyromagnetic
ratio of the nuclei

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that you're looking at.

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And we're going to talk
about hydrogen today.

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And so you've got to be able to
synthesize precise frequencies

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with precise durations
and power levels

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in order to send
those to your sample.

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So you've got this console.

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It's got amplifiers in there.

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100-watt amplifiers is
pretty much the standard.

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Actually, I shouldn't even
say that's the standard.

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I think ours have 500-watt
amplifiers in there.

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You've got different boards.

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It used to be that
these all were

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plugged in to these long
things with connections.

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And it talked through what was
called a backplane, but, now

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that these are modern
digital consoles,

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it all talks via ethernet.

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So everything has an address,
and it talks to each other.

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It routes the signal to
where it needs to go.

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You've also got some
preamplifiers here.

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So all this material
or everything

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that's in the console
will generate the signal

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that is sent to
your sample in order

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to excite it the way
that you need to in order

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to get the information
out that you want to.

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This also will take the signal
that your sample gives off.

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And it will amplify it and
digitize it and send it

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to the computer so that
it can be processed

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into something you can use.

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To send the sample--
well, so the console

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generates all that
signal, but it's

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got to be broadcast to
your sample somehow.

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And so we think of the
probe as the NMR antenna.

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So probes can come in a
number of different formats.

247
00:13:16,160 --> 00:13:19,600
There can be probes
for looking at solids.

248
00:13:19,600 --> 00:13:23,050
So you wouldn't even dissolve
your sample in a liquid.

249
00:13:23,050 --> 00:13:25,420
There can be what are
called flow probes where

250
00:13:25,420 --> 00:13:26,490
you've got just--

251
00:13:26,490 --> 00:13:28,780
we call it a cell, but
it's just a container

252
00:13:28,780 --> 00:13:30,250
that's a certain volume.

253
00:13:30,250 --> 00:13:34,210
And you pump your sample up
through a tube into that cell,

254
00:13:34,210 --> 00:13:36,710
analyze it, and then
you pump it out.

255
00:13:36,710 --> 00:13:39,340
There's what we call a
micro coil probe, which

256
00:13:39,340 --> 00:13:40,580
just has a small cell.

257
00:13:40,580 --> 00:13:43,430
So I've used ones or had them
in the past in other labs

258
00:13:43,430 --> 00:13:45,680
where it had a 5
microliter cell.

259
00:13:45,680 --> 00:13:48,550
So you could look at just a
very small amount of things.

260
00:13:48,550 --> 00:13:52,390
There are also probes that
are known as cryogenic probes.

261
00:13:52,390 --> 00:13:55,270
Those, the electronics
that are in the probe

262
00:13:55,270 --> 00:13:59,000
are held at liquid helium or
liquid nitrogen temperature.

263
00:13:59,000 --> 00:14:03,338
And, by doing that, it cuts down
on the inherent electric noise

264
00:14:03,338 --> 00:14:04,630
that's present in the circuits.

265
00:14:04,630 --> 00:14:06,930
And it makes them
more sensitive.

266
00:14:06,930 --> 00:14:08,862
So I've brought a probe
here, and you're not

267
00:14:08,862 --> 00:14:11,320
going to be able to see this
from where you're sitting back

268
00:14:11,320 --> 00:14:14,080
there, but you can come up and
look at it later if you want.

269
00:14:14,080 --> 00:14:17,470
Your benchtop instrument will
have the same stuff in it.

270
00:14:17,470 --> 00:14:20,280
It's just not going to
look like this exactly.

271
00:14:20,280 --> 00:14:23,950
So this is what gets inserted up
from the bottom of the magnet.

272
00:14:23,950 --> 00:14:26,200
And it's just-- it's
screwed in, and it stays

273
00:14:26,200 --> 00:14:27,520
in the bottom of the magnet.

274
00:14:27,520 --> 00:14:30,040
There's only a
couple of connections

275
00:14:30,040 --> 00:14:34,450
where the wires from the
console are hooked up to this.

276
00:14:34,450 --> 00:14:37,180
And so this one, I can
take the cover off of.

277
00:14:37,180 --> 00:14:39,730
And you can look at
this when you come up.

278
00:14:39,730 --> 00:14:45,100
Up in the very top of the probe,
there's a little glass insert.

279
00:14:45,100 --> 00:14:47,350
And there's some
flat ribbons of wire

280
00:14:47,350 --> 00:14:48,850
that are wound around here.

281
00:14:48,850 --> 00:14:50,270
And so I've got
that pointed out.

282
00:14:50,270 --> 00:14:53,350
In fact, I think that's the same
probe that I took a picture of.

283
00:14:53,350 --> 00:14:58,670
And so your sample
will go down, and it

284
00:14:58,670 --> 00:15:04,020
will go right into where
those coils of wire are.

285
00:15:04,020 --> 00:15:06,910
And so the coils of wire
will send the signal

286
00:15:06,910 --> 00:15:10,090
to your sample that's being
generated in the console.

287
00:15:10,090 --> 00:15:12,250
And then, when that
signal gets turned off,

288
00:15:12,250 --> 00:15:15,830
your sample will relax back
to its equilibrium state.

289
00:15:15,830 --> 00:15:18,340
And it will induce
a small voltage

290
00:15:18,340 --> 00:15:21,430
in these coils, which
gets picked up, sent back

291
00:15:21,430 --> 00:15:23,680
through that console
and off to the computer

292
00:15:23,680 --> 00:15:26,630
to generate your spectrum.

293
00:15:26,630 --> 00:15:28,030
So I will leave this right here.

294
00:15:28,030 --> 00:15:30,940
If you come up later to look
at it, feel free to pick it up.

295
00:15:30,940 --> 00:15:31,940
Just be very careful.

296
00:15:31,940 --> 00:15:32,680
This is glass.

297
00:15:32,680 --> 00:15:35,780
And you don't want to bang on
it or bend it because it will--

298
00:15:35,780 --> 00:15:39,070
you can break it, not that
it's working anyways anymore,

299
00:15:39,070 --> 00:15:41,803
but we like to have
it for demonstrations.

300
00:15:44,980 --> 00:15:48,880
OK, so the NMR signal
itself, it's generated

301
00:15:48,880 --> 00:15:51,040
when a collection of
nuclei, meaning your sample,

302
00:15:51,040 --> 00:15:53,440
is placed in a
strong magnetic field

303
00:15:53,440 --> 00:15:56,800
and irradiated with
radio frequency energy

304
00:15:56,800 --> 00:15:58,180
of the appropriate frequency.

305
00:15:58,180 --> 00:16:00,790
And we'll see what
that is in a second.

306
00:16:00,790 --> 00:16:03,190
The signal is a very
small amount of energy

307
00:16:03,190 --> 00:16:07,600
that's given off, as the nuclei
in your sample transition

308
00:16:07,600 --> 00:16:10,130
back to their equilibrium state.

309
00:16:10,130 --> 00:16:12,850
And it's really-- it's a
time-dependent current that's

310
00:16:12,850 --> 00:16:17,890
induced in the coil in the probe
on the order of microvolts.

311
00:16:21,400 --> 00:16:25,900
So it possesses four different--
four properties and only

312
00:16:25,900 --> 00:16:28,420
four properties
that we make use of.

313
00:16:28,420 --> 00:16:32,590
So pictured right here
is an actual NMR signal.

314
00:16:32,590 --> 00:16:35,230
It's what we call a
free induction decay.

315
00:16:35,230 --> 00:16:38,530
It's just a damped sinusoid.

316
00:16:38,530 --> 00:16:44,540
And, out of that, you can
get these four properties

317
00:16:44,540 --> 00:16:46,610
that you can make use of.

318
00:16:46,610 --> 00:16:51,780
The one that we usually make the
most use of is the frequency.

319
00:16:51,780 --> 00:16:54,050
And so I'll tell you
how you can convert this

320
00:16:54,050 --> 00:16:57,590
to this in a few
slides, but where

321
00:16:57,590 --> 00:17:00,920
lines will appear on
this graph tells us

322
00:17:00,920 --> 00:17:03,590
something about the
molecular environment

323
00:17:03,590 --> 00:17:08,180
that whatever gave rise
to that signal is in.

324
00:17:08,180 --> 00:17:12,109
So that's when-- most of the
time, that's what you use.

325
00:17:12,109 --> 00:17:15,170
The next most common piece of
information you use out of it

326
00:17:15,170 --> 00:17:16,700
is the intensity.

327
00:17:16,700 --> 00:17:20,780
So the intensity of a
resonance in the NMR spectrum

328
00:17:20,780 --> 00:17:24,680
is going to be directly
proportional to the number

329
00:17:24,680 --> 00:17:29,510
of nuclei that give
rise to that signal.

330
00:17:29,510 --> 00:17:31,970
And that doesn't
mean just-- well,

331
00:17:31,970 --> 00:17:34,910
it also means just every
nuclei that's in there,

332
00:17:34,910 --> 00:17:37,580
but specifically, for
instance, if you've

333
00:17:37,580 --> 00:17:41,870
got one signal from this group
of protons and one signal

334
00:17:41,870 --> 00:17:44,450
from this group of
protons, their intensity

335
00:17:44,450 --> 00:17:47,690
is going to be equal because
three protons gave rise

336
00:17:47,690 --> 00:17:50,180
to this signal,
and three protons

337
00:17:50,180 --> 00:17:51,990
gave rise to that signal.

338
00:17:51,990 --> 00:17:56,270
So you can use that as an
internal check in molecules

339
00:17:56,270 --> 00:18:00,240
to make sure that you're
identifying peaks correctly.

340
00:18:00,240 --> 00:18:05,420
You can also use it to quantify
molecules, different molecules

341
00:18:05,420 --> 00:18:08,420
that are present in a sample.

342
00:18:08,420 --> 00:18:11,240
And you can even
make a sample where

343
00:18:11,240 --> 00:18:14,960
you've spiked a known
amount of something in there

344
00:18:14,960 --> 00:18:17,420
to serve as a standard
and then quantify

345
00:18:17,420 --> 00:18:20,990
the amount of an unknown
that you've put in there.

346
00:18:20,990 --> 00:18:23,940
Another property is the
phase of this signal.

347
00:18:23,940 --> 00:18:26,660
So what I'm showing
here is not something

348
00:18:26,660 --> 00:18:27,830
you're going to acquire.

349
00:18:27,830 --> 00:18:30,320
It's called a
two-dimensional spectrum,

350
00:18:30,320 --> 00:18:34,080
but what I'm trying to highlight
is that each of these colors,

351
00:18:34,080 --> 00:18:34,580
be it--

352
00:18:34,580 --> 00:18:35,420
I called it red--

353
00:18:35,420 --> 00:18:39,110
I think it might be some
blend of that or blue--

354
00:18:39,110 --> 00:18:41,060
are a different phase.

355
00:18:41,060 --> 00:18:43,220
Specifically, think of this.

356
00:18:43,220 --> 00:18:45,620
Does anybody know what a
two-dimensional map is?

357
00:18:45,620 --> 00:18:47,420
Ever look at a
topographic map where

358
00:18:47,420 --> 00:18:52,040
you've got mountains that
are outlined by contours?

359
00:18:52,040 --> 00:18:53,178
So you can think--

360
00:18:53,178 --> 00:18:53,970
what did I call it?

361
00:18:53,970 --> 00:18:55,220
So I said blue is negative.

362
00:18:55,220 --> 00:18:58,080
So think of the negative--

363
00:18:58,080 --> 00:19:02,270
think of the blue cross peaks
as being holes or going down

364
00:19:02,270 --> 00:19:02,960
into the plane.

365
00:19:02,960 --> 00:19:06,270
And think of the red ones
coming out of the plane.

366
00:19:06,270 --> 00:19:11,660
So the way that this
experiment is acquired,

367
00:19:11,660 --> 00:19:15,980
it makes methylene groups
have a negative phase.

368
00:19:15,980 --> 00:19:19,940
And it makes methyl and methine
groups have a positive phase.

369
00:19:19,940 --> 00:19:22,970
So that's really useful when
you're looking at an unknown

370
00:19:22,970 --> 00:19:25,440
because, right off the
bat, you can just say,

371
00:19:25,440 --> 00:19:27,530
OK, I know that this,
this, this, and this

372
00:19:27,530 --> 00:19:29,390
are from a methyl or methine.

373
00:19:29,390 --> 00:19:32,420
And I know that these blue
peaks are from methylenes.

374
00:19:32,420 --> 00:19:34,130
And then, specifically,
I can look at it

375
00:19:34,130 --> 00:19:36,680
and say, OK, since this one
and this one are in a line

376
00:19:36,680 --> 00:19:38,420
next to each other,
I know that these

377
00:19:38,420 --> 00:19:41,990
are protons on the same carbon.

378
00:19:41,990 --> 00:19:46,010
The last piece of information
that comes out of an NMR signal

379
00:19:46,010 --> 00:19:47,630
is the duration of the decay.

380
00:19:47,630 --> 00:19:49,020
So it can be longer.

381
00:19:49,020 --> 00:19:50,270
It can be shorter.

382
00:19:50,270 --> 00:19:53,480
You can use that like
for things like I hinted

383
00:19:53,480 --> 00:19:55,820
at before where you
have-- small molecules

384
00:19:55,820 --> 00:19:58,580
usually have a long decay.

385
00:19:58,580 --> 00:20:01,320
Large molecules usually
have a very short decay.

386
00:20:01,320 --> 00:20:04,490
So, if you have a protein
that's binding a small molecule

387
00:20:04,490 --> 00:20:09,170
substrate, its decay is going
to transition from something

388
00:20:09,170 --> 00:20:10,520
long to something short.

389
00:20:10,520 --> 00:20:14,150
And you can use that to
tell that your molecule has

390
00:20:14,150 --> 00:20:16,080
been bound.

391
00:20:16,080 --> 00:20:19,646
Any questions?

392
00:20:19,646 --> 00:20:23,650
All right, so unfortunately
not all nuclei

393
00:20:23,650 --> 00:20:26,650
can be measured by NMR.

394
00:20:26,650 --> 00:20:30,340
Any nucleus that
possesses angular momentum

395
00:20:30,340 --> 00:20:33,010
will exhibit a magnetic
moment that will

396
00:20:33,010 --> 00:20:37,000
interact with a magnetic field.

397
00:20:37,000 --> 00:20:38,590
Just like electrons,
if you've learned

398
00:20:38,590 --> 00:20:41,890
about in general chemistry where
you learned the quantum numbers

399
00:20:41,890 --> 00:20:45,960
and you learned about spin,
it's the same for nuclei.

400
00:20:45,960 --> 00:20:48,610
So we say a nucleus possesses
spin in reference to its spin

401
00:20:48,610 --> 00:20:52,210
quantum number,
which is labeled I.

402
00:20:52,210 --> 00:20:56,170
It's easy to think of nuclei
as cute little balls that

403
00:20:56,170 --> 00:21:00,130
are rotating around, but
remember they're not spinning.

404
00:21:00,130 --> 00:21:02,650
It's just an inherent
physical property

405
00:21:02,650 --> 00:21:05,860
that seems like they're
little spinning balls when

406
00:21:05,860 --> 00:21:06,880
they're not.

407
00:21:06,880 --> 00:21:09,460
So there are rules for
determining if a nucleus has

408
00:21:09,460 --> 00:21:11,230
spin or not.

409
00:21:11,230 --> 00:21:15,760
It's present in either half
integer or integer values.

410
00:21:15,760 --> 00:21:18,680
You don't really have to worry
about that for this class.

411
00:21:18,680 --> 00:21:22,930
We're going to be looking at
spin 1/2 nuclei protons, which

412
00:21:22,930 --> 00:21:25,630
are the easiest to interpret.

413
00:21:25,630 --> 00:21:31,840
And luckily protons have a
99.9885% natural abundance.

414
00:21:31,840 --> 00:21:37,360
So it's the most sensitive
and strongest NMR signal

415
00:21:37,360 --> 00:21:41,350
that you can get
out of any nucleus.

416
00:21:41,350 --> 00:21:42,940
There are, like
I said, the rules

417
00:21:42,940 --> 00:21:46,000
for determining whether
something has spin.

418
00:21:46,000 --> 00:21:47,650
Nuclei with even protons--

419
00:21:47,650 --> 00:21:50,980
an even number of protons and
an even number of neutrons

420
00:21:50,980 --> 00:21:52,850
do not have nuclear spin.

421
00:21:52,850 --> 00:21:55,930
And so they're NMR inactive.

422
00:21:55,930 --> 00:21:58,930
Unfortunately, the
next most common thing

423
00:21:58,930 --> 00:22:02,560
that we would love to look at
as organic chemists is carbon.

424
00:22:02,560 --> 00:22:07,450
And carbon has six protons and
six neutrons for carbon-12.

425
00:22:07,450 --> 00:22:08,920
And so we can't.

426
00:22:08,920 --> 00:22:11,050
It's NMR inactive.

427
00:22:11,050 --> 00:22:14,080
Luckily for us,
though, carbon has

428
00:22:14,080 --> 00:22:19,330
an isotope that's 1.1% naturally
abundant, which is C-13.

429
00:22:19,330 --> 00:22:21,250
And we can look at that.

430
00:22:21,250 --> 00:22:23,890
We take a hit on
sensitivity, but we can still

431
00:22:23,890 --> 00:22:25,300
get an NMR spectrum of that.

432
00:22:25,300 --> 00:22:27,190
So that's good.

433
00:22:27,190 --> 00:22:31,270
Some nuclei have multiple
NMR-active isotopes.

434
00:22:31,270 --> 00:22:34,330
That doesn't mean they always
appear in the same spectrum.

435
00:22:34,330 --> 00:22:38,270
They will have different
gyromagnetic ratios.

436
00:22:38,270 --> 00:22:41,350
So they will appear at
different overall frequencies,

437
00:22:41,350 --> 00:22:43,720
but you can look
at-- sometimes, you

438
00:22:43,720 --> 00:22:45,100
can use that to your advantage.

439
00:22:45,100 --> 00:22:48,310
You could take a
spectrum of 10 boron

440
00:22:48,310 --> 00:22:50,860
and a separate
spectrum of 11 boron.

441
00:22:50,860 --> 00:22:56,200
Or a proton, we use the
signal from deuterium

442
00:22:56,200 --> 00:23:03,400
as a lock signal for the magnet
to focus on and counteract

443
00:23:03,400 --> 00:23:04,420
its inherent drift.

444
00:23:08,920 --> 00:23:13,450
So what's the physical
basis of the NMR signal?

445
00:23:13,450 --> 00:23:16,810
In a magnetic field, all
those little magnetic moments

446
00:23:16,810 --> 00:23:19,630
are going to adopt
an orientation

447
00:23:19,630 --> 00:23:22,880
relative to that field.

448
00:23:22,880 --> 00:23:25,220
The allowed orientation
of these moments

449
00:23:25,220 --> 00:23:27,260
is going to be explained
by quantum mechanics.

450
00:23:27,260 --> 00:23:30,890
Luckily, we don't have
to really get into that.

451
00:23:30,890 --> 00:23:34,100
And the process that nuclei
undergo during an experiment

452
00:23:34,100 --> 00:23:35,640
can be rationalized in two ways.

453
00:23:35,640 --> 00:23:37,430
You can think of it
in terms of vectors,

454
00:23:37,430 --> 00:23:40,310
so which way those little
magnetic fields are pointing,

455
00:23:40,310 --> 00:23:43,430
or you can think of it in
terms of the energy levels

456
00:23:43,430 --> 00:23:45,530
that the nuclei
adopt when they're

457
00:23:45,530 --> 00:23:48,120
put in that magnetic field.

458
00:23:48,120 --> 00:23:50,630
So I tried to make a
little cartoon here.

459
00:23:50,630 --> 00:23:52,160
With no magnetic
field, these are

460
00:23:52,160 --> 00:23:54,920
supposed to just be
all randomly oriented,

461
00:23:54,920 --> 00:23:58,760
but, when I immerse my
collection of molecules that's

462
00:23:58,760 --> 00:24:00,950
in my sample in
a magnetic field,

463
00:24:00,950 --> 00:24:04,790
they will line up and
be either with the field

464
00:24:04,790 --> 00:24:07,970
or against the field.

465
00:24:07,970 --> 00:24:10,790
And so, if we look
at one nucleus

466
00:24:10,790 --> 00:24:13,160
when we place it in
a magnetic field,

467
00:24:13,160 --> 00:24:15,740
quantum mechanics tells
us that it's not just

468
00:24:15,740 --> 00:24:17,570
going to point straight up.

469
00:24:17,570 --> 00:24:21,290
There's got to be some
uncertainty in where

470
00:24:21,290 --> 00:24:23,250
that nucleus is pointing.

471
00:24:23,250 --> 00:24:26,450
And so it is going
to precess, meaning

472
00:24:26,450 --> 00:24:31,040
it's going to rotate around, the
direction of the magnetic field

473
00:24:31,040 --> 00:24:33,590
with a characteristic
frequency, which

474
00:24:33,590 --> 00:24:35,090
we call the Larmor frequency.

475
00:24:35,090 --> 00:24:36,470
It's named for--
what's his name?

476
00:24:36,470 --> 00:24:38,930
Joseph Larmor who
was a physicist

477
00:24:38,930 --> 00:24:41,840
back in the late
1800s, early 1900s.

478
00:24:41,840 --> 00:24:43,880
That frequency is
going to be directly

479
00:24:43,880 --> 00:24:46,760
proportional to the
strength of the magnet

480
00:24:46,760 --> 00:24:50,780
that you put your sample in.

481
00:24:50,780 --> 00:24:54,980
I've unfortunately--
so gyromagnetic ratio

482
00:24:54,980 --> 00:24:58,640
can be specified in either
radians per second per tesla

483
00:24:58,640 --> 00:25:00,500
or in hertz per tesla.

484
00:25:00,500 --> 00:25:04,040
I apologize for not being too
careful in that I will jump

485
00:25:04,040 --> 00:25:07,340
back and forth between the two.

486
00:25:07,340 --> 00:25:13,330
And so, for a proton, if we take
a magnet, that's 11.75 tesla

487
00:25:13,330 --> 00:25:16,420
and we put our
sample in there, it's

488
00:25:16,420 --> 00:25:20,110
going to precess around
the field at 500 megahertz.

489
00:25:20,110 --> 00:25:22,690
And so, when we talk
about NMR instruments,

490
00:25:22,690 --> 00:25:26,210
just as far as
what size they are,

491
00:25:26,210 --> 00:25:30,970
they are not specified by
the strength of their magnet.

492
00:25:30,970 --> 00:25:33,250
They're specified
by the frequency

493
00:25:33,250 --> 00:25:36,220
that a proton
precesses in a field

494
00:25:36,220 --> 00:25:37,580
with a magnet of that strength.

495
00:25:37,580 --> 00:25:41,320
So, if you come down to the
DCIF, I'll say I have a 500,

496
00:25:41,320 --> 00:25:43,990
or I have a 600,
or I have a 400.

497
00:25:43,990 --> 00:25:46,960
In the undergraduate teaching
labs, you have a 300.

498
00:25:46,960 --> 00:25:49,780
And I think the benchtop
is a 60 megahertz.

499
00:25:49,780 --> 00:25:52,930
And I'd have to go
look up in a table

500
00:25:52,930 --> 00:25:56,590
or do the calculation
how strong in tesla

501
00:25:56,590 --> 00:26:01,480
a 60 megahertz NMR
magnet is, but that's

502
00:26:01,480 --> 00:26:02,650
the way it's specified.

503
00:26:02,650 --> 00:26:04,720
So that's for one
nuclei when you put it

504
00:26:04,720 --> 00:26:10,570
in the magnetic field,
but our sample is actually

505
00:26:10,570 --> 00:26:12,070
a bunch of different nuclei.

506
00:26:12,070 --> 00:26:14,280
Or not-- well, yes, it's a
bunch of different nuclei.

507
00:26:14,280 --> 00:26:16,480
It's a collection of nuclei.

508
00:26:16,480 --> 00:26:21,160
We don't have to keep track
of every individual nucleus

509
00:26:21,160 --> 00:26:22,690
and deal with the
quantum mechanics

510
00:26:22,690 --> 00:26:24,760
when we look at
an NMR experiment.

511
00:26:24,760 --> 00:26:29,720
We can treat the whole sample
as a collection of the nuclei,

512
00:26:29,720 --> 00:26:33,430
so summing up all the individual
magnetic moments, and just

513
00:26:33,430 --> 00:26:35,470
look at the bulk magnetization.

514
00:26:35,470 --> 00:26:38,260
And so we can use statistical
mechanics in order

515
00:26:38,260 --> 00:26:41,030
to figure out what's going on.

516
00:26:41,030 --> 00:26:43,120
So we put our nucleus--

517
00:26:43,120 --> 00:26:44,200
here's our sample.

518
00:26:44,200 --> 00:26:47,680
We've got, say, 10
milligrams of material.

519
00:26:47,680 --> 00:26:50,530
We've got it dissolved
in about 600 microliters

520
00:26:50,530 --> 00:26:52,060
of a deuterated solvent.

521
00:26:52,060 --> 00:26:55,540
We drop it down so it goes
in our probe in the magnet.

522
00:26:55,540 --> 00:26:57,970
And our collection
of nuclei will

523
00:26:57,970 --> 00:27:01,450
start precessing either
aligned with the field

524
00:27:01,450 --> 00:27:04,850
or aligned opposite the field.

525
00:27:04,850 --> 00:27:08,860
So there will be a slight
energetic preference

526
00:27:08,860 --> 00:27:13,060
for those nuclei to have
their magnetic moment aligned

527
00:27:13,060 --> 00:27:14,890
with the field.

528
00:27:14,890 --> 00:27:17,530
And that population
difference will

529
00:27:17,530 --> 00:27:20,020
result in this net
magnetization that we

530
00:27:20,020 --> 00:27:23,626
call the bulk magnetization.

531
00:27:23,626 --> 00:27:24,850
Let me put that down.

532
00:27:27,440 --> 00:27:31,100
We can jump from
thinking of vectors

533
00:27:31,100 --> 00:27:33,020
to thinking of energy levels.

534
00:27:33,020 --> 00:27:36,200
So everything that is
aligned with the field

535
00:27:36,200 --> 00:27:39,170
is going to be at a
lower energy level.

536
00:27:39,170 --> 00:27:43,310
And we call that just
the plus 1/2 nuclei.

537
00:27:43,310 --> 00:27:45,740
And everything that is
aligned against the field

538
00:27:45,740 --> 00:27:49,670
is going to be at a higher
energy level at negative 1/2.

539
00:27:49,670 --> 00:27:54,080
And so the difference
between these two levels

540
00:27:54,080 --> 00:27:58,970
is going to increase as the
strength of the magnetic field

541
00:27:58,970 --> 00:28:00,950
increases.

542
00:28:00,950 --> 00:28:03,560
And so maybe over here,
on the 60 megahertz,

543
00:28:03,560 --> 00:28:05,340
the difference is
only that much,

544
00:28:05,340 --> 00:28:09,230
but, when you get to our
600, it's a lot more.

545
00:28:09,230 --> 00:28:12,620
Here's where the measurement--
or the principle behind the NMR

546
00:28:12,620 --> 00:28:13,610
measurement comes in.

547
00:28:13,610 --> 00:28:18,140
You're making nuclei transition
from one energy level

548
00:28:18,140 --> 00:28:19,730
to the other energy level.

549
00:28:19,730 --> 00:28:23,690
So you're perturbing their
equilibrium distribution,

550
00:28:23,690 --> 00:28:26,180
and then you're letting
them relax back.

551
00:28:26,180 --> 00:28:28,280
And that's what
gives off the signal

552
00:28:28,280 --> 00:28:29,580
that we make use of in NMR.

553
00:28:32,340 --> 00:28:36,020
So I guess I jumped too
far ahead in my verbiage.

554
00:28:36,020 --> 00:28:39,310
So we have our sample in there.

555
00:28:39,310 --> 00:28:40,570
It's lined up.

556
00:28:40,570 --> 00:28:43,180
And we perturb it
with an RF pulse.

557
00:28:43,180 --> 00:28:45,580
So now I've jump
back to vectors.

558
00:28:45,580 --> 00:28:50,440
If you think of it in terms
of vectors, when you generate

559
00:28:50,440 --> 00:28:52,870
that radio frequency
pulse that has

560
00:28:52,870 --> 00:28:55,330
the frequency equal to the
difference in those energy

561
00:28:55,330 --> 00:28:59,170
levels, you are, in
essence, generating

562
00:28:59,170 --> 00:29:01,810
a small magnetic
field that is aligned.

563
00:29:01,810 --> 00:29:03,700
In this case, it's
arbitrary, but we'll

564
00:29:03,700 --> 00:29:06,160
say it's aligned
along the x-axis.

565
00:29:06,160 --> 00:29:09,190
That acts to topple--

566
00:29:09,190 --> 00:29:13,210
or not topple, tip this bulk
magnetization vector off

567
00:29:13,210 --> 00:29:17,830
of being pointed with the main
field over into the xy-plane.

568
00:29:17,830 --> 00:29:24,560
It's still precessing around at
that characteristic frequency.

569
00:29:24,560 --> 00:29:27,730
And, when it has a
component in the xy-plane,

570
00:29:27,730 --> 00:29:31,690
that will generate a current
in these little coils

571
00:29:31,690 --> 00:29:35,650
in the probe, which is then
received back at the console

572
00:29:35,650 --> 00:29:37,610
and sent to the computer.

573
00:29:37,610 --> 00:29:40,450
So we pulse our sample.

574
00:29:40,450 --> 00:29:43,518
And depending on how long
we turn on that pulse for--

575
00:29:43,518 --> 00:29:45,310
and it's usually the
order of microseconds.

576
00:29:45,310 --> 00:29:48,790
I think our pulses are set up
to be about 10 microseconds.

577
00:29:48,790 --> 00:29:53,420
We can tip this over
to some varying degree.

578
00:29:53,420 --> 00:29:55,360
And so usually we
try and tip it over

579
00:29:55,360 --> 00:29:59,740
by a specific amount, which is
a 90-degree pulse, because that

580
00:29:59,740 --> 00:30:04,060
will generate the maximum amount
of signal that we can get out.

581
00:30:04,060 --> 00:30:06,070
So we tip it over
into the xy-plane.

582
00:30:06,070 --> 00:30:08,320
We turn off that pulse.

583
00:30:08,320 --> 00:30:11,020
And then we let it relax,
and we collect our signal.

584
00:30:13,625 --> 00:30:15,750
Our signal-- I think I said
this before-- is called

585
00:30:15,750 --> 00:30:17,250
the free induction decay.

586
00:30:17,250 --> 00:30:19,380
And so here's another
diagram of it.

587
00:30:19,380 --> 00:30:21,640
We've turned off that pulse.

588
00:30:21,640 --> 00:30:23,500
The signal is
precessing here, but it

589
00:30:23,500 --> 00:30:26,020
relaxes back so that
the component here

590
00:30:26,020 --> 00:30:28,300
gets shorter and shorter
while we grow back

591
00:30:28,300 --> 00:30:30,490
the component in
the z-direction.

592
00:30:30,490 --> 00:30:32,200
That gives us this voltage--

593
00:30:32,200 --> 00:30:33,680
and my laser died--

594
00:30:33,680 --> 00:30:36,680
that gets picked up in the coil.

595
00:30:36,680 --> 00:30:39,770
We can do that multiple times.

596
00:30:39,770 --> 00:30:41,260
So, if you've got
a strong sample,

597
00:30:41,260 --> 00:30:43,870
you can just take
one scan, but usually

598
00:30:43,870 --> 00:30:45,940
we'll take multiple
scans because you

599
00:30:45,940 --> 00:30:48,550
can do what's called
signal averaging, which

600
00:30:48,550 --> 00:30:51,380
is add them together.

601
00:30:51,380 --> 00:30:55,540
And that can help you remove
artifacts, increase your signal

602
00:30:55,540 --> 00:30:58,365
to noise, and other things.

603
00:30:58,365 --> 00:30:59,740
So that's what
the free induction

604
00:30:59,740 --> 00:31:02,920
decay is in the NMR signal.

605
00:31:02,920 --> 00:31:09,970
I put this back in my slide
pack after I gave the slides

606
00:31:09,970 --> 00:31:11,290
to Professor Dolhun to print.

607
00:31:11,290 --> 00:31:14,440
So you don't have this in
your handouts unfortunately.

608
00:31:14,440 --> 00:31:15,580
This is just--

609
00:31:15,580 --> 00:31:18,280
I was thinking this
is still a good way

610
00:31:18,280 --> 00:31:21,220
to show about the NMR signal,
but in terms of the number

611
00:31:21,220 --> 00:31:23,450
of spins and the energy levels.

612
00:31:23,450 --> 00:31:25,960
So here's your equilibrium.

613
00:31:25,960 --> 00:31:28,360
You've got more spins pointing.

614
00:31:28,360 --> 00:31:31,300
I'm saying they're pointing
down in this lower energy level.

615
00:31:31,300 --> 00:31:35,290
You pulse it, and that
equalizes the energy level.

616
00:31:35,290 --> 00:31:37,360
So I forget how
many are in each,

617
00:31:37,360 --> 00:31:39,800
but these are supposed to be
an equal number of arrows.

618
00:31:39,800 --> 00:31:42,880
Then, after you
turn off that pulse,

619
00:31:42,880 --> 00:31:46,630
the spins that got transitioned
to the upper energy level

620
00:31:46,630 --> 00:31:48,310
will relax back down.

621
00:31:48,310 --> 00:31:49,870
So there's a
predominantly-- they're

622
00:31:49,870 --> 00:31:52,780
more predominantly in the lower
energy than the upper energy.

623
00:31:52,780 --> 00:31:58,160
As they do that, they give
off the free induction decay,

624
00:31:58,160 --> 00:32:01,490
which is your NMR signal.

625
00:32:01,490 --> 00:32:02,490
Are these any questions?

626
00:32:07,390 --> 00:32:11,146
OK, so what do we
do with that FID?

627
00:32:11,146 --> 00:32:12,650
Now, I've been doing this--

628
00:32:12,650 --> 00:32:14,920
I don't know-- since 1999.

629
00:32:14,920 --> 00:32:16,390
I can look at an FID.

630
00:32:16,390 --> 00:32:18,370
I can say, well,
that's a long one.

631
00:32:18,370 --> 00:32:20,320
I can look at an
FID and say, yeah,

632
00:32:20,320 --> 00:32:23,380
that's got several different
frequencies in there.

633
00:32:23,380 --> 00:32:25,610
But, as far as looking
at an FID and saying,

634
00:32:25,610 --> 00:32:28,810
oh, that comes from DMF or, oh,
that comes from ethyl acetate,

635
00:32:28,810 --> 00:32:30,850
no, I can't do that.

636
00:32:30,850 --> 00:32:32,830
And I doubt that
anybody else could.

637
00:32:32,830 --> 00:32:38,000
So we have to transform that
and somehow make sense of it.

638
00:32:38,000 --> 00:32:41,540
And so that is done using
a Fourier transform.

639
00:32:41,540 --> 00:32:44,680
And so a Fourier
transform takes something

640
00:32:44,680 --> 00:32:47,890
that is in the time domain.

641
00:32:47,890 --> 00:32:52,300
And it transforms it to
the frequency domain.

642
00:32:52,300 --> 00:32:56,770
And, a long time ago, before
the advent of computers,

643
00:32:56,770 --> 00:33:00,880
NMR wasn't done using Fourier
transforms because it was

644
00:33:00,880 --> 00:33:03,080
computationally too difficult.

645
00:33:03,080 --> 00:33:06,160
And so someone
back in the '60s--

646
00:33:06,160 --> 00:33:08,800
actually, someone famous
at IBM developed a way

647
00:33:08,800 --> 00:33:10,880
to do this to make it
a little bit easier,

648
00:33:10,880 --> 00:33:12,820
but they still had to
print out little cards.

649
00:33:12,820 --> 00:33:14,110
And you'd punch holes in them.

650
00:33:14,110 --> 00:33:17,410
And it would take days and
days to feed it into a machine.

651
00:33:17,410 --> 00:33:19,960
And nowadays your
phone can do it.

652
00:33:19,960 --> 00:33:21,398
It's got more
computational power

653
00:33:21,398 --> 00:33:22,940
than something that
had a whole room.

654
00:33:22,940 --> 00:33:26,080
So everything is done by
Fourier transform now.

655
00:33:26,080 --> 00:33:28,600
That gives us our
spectrum, which

656
00:33:28,600 --> 00:33:31,210
consists of lines,
which we can look at,

657
00:33:31,210 --> 00:33:35,790
and we can interpret
and figure out.

658
00:33:35,790 --> 00:33:38,850
And, no, I couldn't do a
Fourier transform or solve one

659
00:33:38,850 --> 00:33:40,890
in my head or even on paper.

660
00:33:40,890 --> 00:33:44,650
So it's just something
the computer does.

661
00:33:44,650 --> 00:33:45,610
So let's back up.

662
00:33:45,610 --> 00:33:48,730
I've given away a lot of this
because I've already showed

663
00:33:48,730 --> 00:33:52,520
you several spectra, and you see
that there are multiple lines.

664
00:33:52,520 --> 00:33:55,450
But here's the free
curve for the equation

665
00:33:55,450 --> 00:33:58,900
for the frequency
being proportional

666
00:33:58,900 --> 00:34:00,430
to the magnetic field strength.

667
00:34:00,430 --> 00:34:04,090
And you might think,
OK, I have protons.

668
00:34:04,090 --> 00:34:08,170
Why don't I just get one
peak because I have protons?

669
00:34:08,170 --> 00:34:10,060
And I would have
one peak for protons

670
00:34:10,060 --> 00:34:12,820
and one peak for other nuclei.

671
00:34:12,820 --> 00:34:16,570
If it did that, I wouldn't be up
here talking to you about this

672
00:34:16,570 --> 00:34:19,389
because, while it might be
a fine and dandy measurement

673
00:34:19,389 --> 00:34:23,500
for a physicist to use,
it'd be useless for us

674
00:34:23,500 --> 00:34:25,330
in chemistry because
we'd only get

675
00:34:25,330 --> 00:34:29,530
one peak for all the different
protons that are in our sample.

676
00:34:29,530 --> 00:34:32,469
Luckily, when you
put your sample

677
00:34:32,469 --> 00:34:37,150
in a magnet, whatever the
local magnetic environment is

678
00:34:37,150 --> 00:34:41,020
that the nuclei
reside in, that is

679
00:34:41,020 --> 00:34:46,659
going to modify the [INAUDIBLE]
or the external field

680
00:34:46,659 --> 00:34:48,940
that those nuclei feel.

681
00:34:48,940 --> 00:34:52,330
And so that's what spreads
out our single signal

682
00:34:52,330 --> 00:34:57,680
from a proton into the different
regions of the spectrum.

683
00:34:57,680 --> 00:34:59,770
So this is supposed
to be ethyl acetate.

684
00:34:59,770 --> 00:35:01,970
I've got a doubly
bound oxygen here.

685
00:35:01,970 --> 00:35:04,600
I've got a single bound oxygen
here, a methylene, methyl,

686
00:35:04,600 --> 00:35:05,730
and methyl.

687
00:35:05,730 --> 00:35:10,510
So oxygen, I think everybody
might know is electronegative.

688
00:35:10,510 --> 00:35:11,410
It's really greedy.

689
00:35:11,410 --> 00:35:13,720
It doesn't like to
share its electrons.

690
00:35:13,720 --> 00:35:16,870
So it pulls electron
density away

691
00:35:16,870 --> 00:35:18,550
from things that are nearby it.

692
00:35:18,550 --> 00:35:21,310
And that's why I've got
these little deltas up here,

693
00:35:21,310 --> 00:35:24,830
indicating the partial
negative charge.

694
00:35:24,830 --> 00:35:27,100
The things that are
bound closest to it

695
00:35:27,100 --> 00:35:30,280
and even further out, they're
going to be more positively

696
00:35:30,280 --> 00:35:32,140
charged or partial
positively charged

697
00:35:32,140 --> 00:35:34,690
than they would have been
because the electron density is

698
00:35:34,690 --> 00:35:36,470
being pulled away from it.

699
00:35:36,470 --> 00:35:39,760
So that's what helps
spread out those signals.

700
00:35:39,760 --> 00:35:42,850
We call this chemical shift.

701
00:35:42,850 --> 00:35:45,550
It's denoted on a
spectrum as ppm.

702
00:35:45,550 --> 00:35:47,810
And, oftentimes, it's
denoted with delta,

703
00:35:47,810 --> 00:35:49,540
not to be confused
with the delta I've

704
00:35:49,540 --> 00:35:51,940
used for the small charges,
but you might see that

705
00:35:51,940 --> 00:35:53,890
on the axis of it.

706
00:35:53,890 --> 00:35:56,650
So anything that can
perturb electron density

707
00:35:56,650 --> 00:36:00,730
will affect we call it the
shielding of the nucleus,

708
00:36:00,730 --> 00:36:05,860
not only electronegative things,
where nuclei are oriented

709
00:36:05,860 --> 00:36:08,800
in relation to double bonds.

710
00:36:08,800 --> 00:36:14,320
In a benzene ring, you've got
the clouds of electron density

711
00:36:14,320 --> 00:36:16,810
in those pi orbitals.

712
00:36:16,810 --> 00:36:21,010
And things that get
oriented directed into that

713
00:36:21,010 --> 00:36:22,060
will be more shielded.

714
00:36:22,060 --> 00:36:25,630
Things that are sticking off
the ring equatorially-- or not

715
00:36:25,630 --> 00:36:28,870
equatorially, but in the
plane will be deshielded.

716
00:36:28,870 --> 00:36:30,312
So that has an effect.

717
00:36:30,312 --> 00:36:32,020
So all these things
will combine together

718
00:36:32,020 --> 00:36:36,150
to spread out what's
in your spectrum.

719
00:36:36,150 --> 00:36:41,890
So here is just a spectrum
of my ethyl acetate.

720
00:36:41,890 --> 00:36:43,490
And so notice I've
spread it out.

721
00:36:43,490 --> 00:36:44,740
Well, I haven't spread it out.

722
00:36:44,740 --> 00:36:49,000
It is spread out into
three separate signals.

723
00:36:49,000 --> 00:36:56,640
You can use NMR solely as
a fingerprint and tabulate.

724
00:36:56,640 --> 00:37:02,268
I know that only such and such
resonances come at 2 point--

725
00:37:02,268 --> 00:37:02,810
I don't know.

726
00:37:02,810 --> 00:37:04,470
We'll call that 2.01.

727
00:37:04,470 --> 00:37:07,720
And so you can go look in
a table and say, oh, well,

728
00:37:07,720 --> 00:37:11,280
this must be from one of these
small subset of molecules

729
00:37:11,280 --> 00:37:14,220
because they only have
something at 2.01.

730
00:37:14,220 --> 00:37:16,350
It's more important to
be able to rationalize

731
00:37:16,350 --> 00:37:19,360
where things appear by--

732
00:37:19,360 --> 00:37:21,630
or yeah, where things
appear on this spectrum

733
00:37:21,630 --> 00:37:23,100
by where they are
in the molecule

734
00:37:23,100 --> 00:37:26,740
because that will help you
analyze the spectrum better.

735
00:37:26,740 --> 00:37:29,550
So, if we look at this,
we've got three peaks.

736
00:37:29,550 --> 00:37:31,800
Now, I talked about
intensity being

737
00:37:31,800 --> 00:37:34,320
one of the properties
of the signal earlier.

738
00:37:34,320 --> 00:37:36,190
I don't know if
you can see this,

739
00:37:36,190 --> 00:37:42,360
but there's a 3.10 under
there, a 3.10 under here,

740
00:37:42,360 --> 00:37:44,830
and a 2 under here.

741
00:37:44,830 --> 00:37:48,900
So that's the relative
intensity of those signals.

742
00:37:48,900 --> 00:37:53,370
Now, one thing that is common
when you're first learning NMR

743
00:37:53,370 --> 00:37:58,560
is to think that the integrals
are dead on exact so that it

744
00:37:58,560 --> 00:38:00,270
should be 3.00.

745
00:38:00,270 --> 00:38:03,780
No, it's going to be close,
but it's not going to be exact.

746
00:38:03,780 --> 00:38:06,180
You've got to take
great care when you're

747
00:38:06,180 --> 00:38:10,320
acquiring the spectrum to
get your integrals to be

748
00:38:10,320 --> 00:38:13,350
as close to perfect.

749
00:38:13,350 --> 00:38:15,370
So we'd call 3.1 3.

750
00:38:15,370 --> 00:38:18,343
So we know-- we can
look at our molecule.

751
00:38:18,343 --> 00:38:19,510
We've got two methyl groups.

752
00:38:19,510 --> 00:38:22,170
So we can guess that these are
both from the methyl groups

753
00:38:22,170 --> 00:38:26,220
because they integrate the 3 and
that this is from the methylene

754
00:38:26,220 --> 00:38:28,140
because it integrates to 2.

755
00:38:28,140 --> 00:38:33,060
So why is this methylene all
the way down at 4 and these

756
00:38:33,060 --> 00:38:34,050
are up here?

757
00:38:34,050 --> 00:38:36,390
Well, what's the
methylene next to?

758
00:38:36,390 --> 00:38:38,260
It's bound straight
to the oxygen.

759
00:38:38,260 --> 00:38:42,180
So the oxygen is withdrawing
the electron density away

760
00:38:42,180 --> 00:38:43,350
from that methylene.

761
00:38:43,350 --> 00:38:48,390
And it is shifting the peak what
we call downfield, which means

762
00:38:48,390 --> 00:38:52,440
to the left on an NMR spectrum.

763
00:38:52,440 --> 00:38:55,110
That's a leftover term
from in the old days

764
00:38:55,110 --> 00:38:56,250
when they would sweep.

765
00:38:56,250 --> 00:38:58,890
You would actually adjust the
frequency-- or not frequency.

766
00:38:58,890 --> 00:39:00,660
You'd adjust the
strength of the magnet.

767
00:39:00,660 --> 00:39:03,450
So anything that was
down in this direction

768
00:39:03,450 --> 00:39:05,760
used a weaker magnetic
field strength.

769
00:39:05,760 --> 00:39:07,830
Anything that was
up in this direction

770
00:39:07,830 --> 00:39:11,100
used a stronger
magnetic field strength.

771
00:39:11,100 --> 00:39:12,450
Nowadays, we don't do that.

772
00:39:12,450 --> 00:39:15,030
The magnet is always
just what the magnet is,

773
00:39:15,030 --> 00:39:16,710
but those terms
are still around.

774
00:39:16,710 --> 00:39:18,360
So anything to the
left is downfield.

775
00:39:18,360 --> 00:39:20,440
Anything to the
right is upfield.

776
00:39:20,440 --> 00:39:22,800
So this one is
deshielded the most.

777
00:39:22,800 --> 00:39:25,290
It is at 4.1.

778
00:39:25,290 --> 00:39:29,940
The next peak is this one.

779
00:39:29,940 --> 00:39:31,500
Now, we've got to choose.

780
00:39:31,500 --> 00:39:34,620
Is it from this methyl,
or is it from this methyl?

781
00:39:34,620 --> 00:39:38,340
And so you would look, and
you'd say, OK, both of these

782
00:39:38,340 --> 00:39:42,000
are bound to carbon, but the
carbon that this one is bound

783
00:39:42,000 --> 00:39:46,350
to is a carbon that is
doubly bound to an oxygen.

784
00:39:46,350 --> 00:39:50,100
So electron density is being
drawn away from that carbon

785
00:39:50,100 --> 00:39:52,530
by the oxygen. So
that's still going

786
00:39:52,530 --> 00:39:55,620
to also have electron
density being pulled away

787
00:39:55,620 --> 00:39:57,570
from this methyl.

788
00:39:57,570 --> 00:40:00,690
And so that's going
to shift it down here.

789
00:40:00,690 --> 00:40:03,450
This carbon is just
bound to a plain carbon

790
00:40:03,450 --> 00:40:06,360
without a double
bound oxygen on it.

791
00:40:06,360 --> 00:40:10,030
And so it's not
deshielded as much.

792
00:40:10,030 --> 00:40:13,170
Although, if I took
a spectrum that had--

793
00:40:13,170 --> 00:40:17,350
so, if I just had an
alkane like pentane

794
00:40:17,350 --> 00:40:19,950
and I looked at the
terminal methyl on pentane,

795
00:40:19,950 --> 00:40:23,940
it would be over here because
it would not be deshielded

796
00:40:23,940 --> 00:40:27,210
at all compared to this.

797
00:40:27,210 --> 00:40:29,130
Another thing you
might be questioning

798
00:40:29,130 --> 00:40:35,910
is, why are these ones
split into multiple peaks,

799
00:40:35,910 --> 00:40:38,948
but this one is
only a single peak?

800
00:40:38,948 --> 00:40:40,740
Let me make sure I kept
my slides in order.

801
00:40:40,740 --> 00:40:41,970
OK, I did.

802
00:40:41,970 --> 00:40:45,480
That is due to what
is called coupling.

803
00:40:45,480 --> 00:40:50,250
So protons that are
bound to a carbon

804
00:40:50,250 --> 00:40:55,050
will, in essence, talk to
protons on neighboring carbons

805
00:40:55,050 --> 00:40:56,640
through the bonds.

806
00:40:56,640 --> 00:41:01,750
And it's called spin-spin
coupling or scalar coupling.

807
00:41:01,750 --> 00:41:06,600
And so you will have
protons split apart

808
00:41:06,600 --> 00:41:08,220
into characteristic patterns.

809
00:41:10,910 --> 00:41:12,230
What else?

810
00:41:12,230 --> 00:41:17,090
So the splitting on
those peaks is not

811
00:41:17,090 --> 00:41:20,420
dependent on the
main field so that,

812
00:41:20,420 --> 00:41:23,540
if I took that ethyl acetate
spectrum-- and I forget

813
00:41:23,540 --> 00:41:24,410
what strength.

814
00:41:24,410 --> 00:41:27,920
I maybe will say I acquired
that at 500 megahertz.

815
00:41:27,920 --> 00:41:31,400
And I measured the difference
between those peaks.

816
00:41:31,400 --> 00:41:32,630
And we'll say it's 8 hertz.

817
00:41:32,630 --> 00:41:34,940
If I take that
molecule, I put it

818
00:41:34,940 --> 00:41:38,870
in a gigahertz machine,
which is twice as strong,

819
00:41:38,870 --> 00:41:43,930
and I measure the splitting,
it'll still be that same value.

820
00:41:43,930 --> 00:41:49,010
So, for simple spectra, the
splitting follows what's called

821
00:41:49,010 --> 00:41:50,720
the n+1 rule.

822
00:41:50,720 --> 00:41:57,200
And so you look at the number of
protons on neighboring carbons,

823
00:41:57,200 --> 00:41:58,520
and you add that up.

824
00:41:58,520 --> 00:42:00,550
So I guess I should have
drawn another molecule.

825
00:42:00,550 --> 00:42:02,280
Where did my chalk go?

826
00:42:02,280 --> 00:42:05,900
So, for instance, we'll
take this one here.

827
00:42:05,900 --> 00:42:11,880
So CH3, I've got two
protons over here.

828
00:42:11,880 --> 00:42:14,670
So it's going to give
me a simple spectrum.

829
00:42:14,670 --> 00:42:20,100
So it's going to be split
by 2 plus 1 equals 3.

830
00:42:20,100 --> 00:42:21,540
And let's see.

831
00:42:21,540 --> 00:42:29,780
I'm going to close this and
bring up my real spectrum.

832
00:42:29,780 --> 00:42:37,060
So this spectrum
is of 3-heptanone.

833
00:42:37,060 --> 00:42:41,240
And the methyl
here and the methyl

834
00:42:41,240 --> 00:42:46,380
here are these two
resonances over there.

835
00:42:46,380 --> 00:42:49,220
And so you can, in
fact, see that those

836
00:42:49,220 --> 00:42:52,490
are split into three
peaks because each of them

837
00:42:52,490 --> 00:42:55,400
has two protons next to it.

838
00:42:55,400 --> 00:42:57,920
Now, not everything
behaves that way.

839
00:42:57,920 --> 00:43:00,680
When you get into more
complicated molecules,

840
00:43:00,680 --> 00:43:06,900
splitting can be completely
non-rationalizable.

841
00:43:06,900 --> 00:43:09,110
So there are several
ways that can happen.

842
00:43:09,110 --> 00:43:12,560
The most common way is, when the
difference in chemical shifts

843
00:43:12,560 --> 00:43:18,050
between two nuclei is not much
bigger than their coupling

844
00:43:18,050 --> 00:43:21,950
constant, you'll just get a
whole bunch of different peaks.

845
00:43:21,950 --> 00:43:24,390
I can drag up an example
of that in a second.

846
00:43:24,390 --> 00:43:25,210
So let's see.

847
00:43:31,320 --> 00:43:33,690
Oops, OK, so that crashed.

848
00:43:33,690 --> 00:43:35,900
Oh well, so I won't do that.

849
00:43:35,900 --> 00:43:38,930
OK, so I've given
you a table in there

850
00:43:38,930 --> 00:43:40,738
that gives some of
the common splitting

851
00:43:40,738 --> 00:43:42,030
patterns that you will observe.

852
00:43:42,030 --> 00:43:42,320
Yes?

853
00:43:42,320 --> 00:43:44,980
AUDIENCE: So what do you mean
when you say simple spectrum?

854
00:43:44,980 --> 00:43:49,420
JOHN GRIMES: A simple spectrum
is where the splitting obeys

855
00:43:49,420 --> 00:43:51,610
this n+1 rule.

856
00:43:51,610 --> 00:43:55,510
And so all the multiplets
will be analyzable that way.

857
00:43:55,510 --> 00:43:57,370
And you'll know it.

858
00:43:57,370 --> 00:43:59,200
If you look at
something and you don't

859
00:43:59,200 --> 00:44:03,370
see these common patterns,
you can automatically

860
00:44:03,370 --> 00:44:07,000
say, OK, there's more complex
splitting that's going on in

861
00:44:07,000 --> 00:44:08,200
or non-first-order.

862
00:44:14,300 --> 00:44:20,390
The intensities of those peaks
in a first-order multiplet

863
00:44:20,390 --> 00:44:23,960
will obey or agree
with the coefficients

864
00:44:23,960 --> 00:44:25,700
of a binomial expansion, i.e.

865
00:44:25,700 --> 00:44:27,660
Pascal's triangle.

866
00:44:27,660 --> 00:44:34,040
So, for n equals 2, you will get
1 to 2 to 1 and, for 3, 1 to 3

867
00:44:34,040 --> 00:44:34,940
to 3 to 1.

868
00:44:34,940 --> 00:44:37,490
So they will obey that.

869
00:44:37,490 --> 00:44:41,450
If it was non-first-order,
you might see four peaks,

870
00:44:41,450 --> 00:44:44,435
but you wouldn't have that
same intensity pattern.

871
00:44:48,810 --> 00:44:53,400
So here's some other
examples of NMR spectra.

872
00:44:53,400 --> 00:44:55,050
Here's a simple one, ethanol.

873
00:44:55,050 --> 00:44:58,440
We can look at this, and we
can rationalize where the peaks

874
00:44:58,440 --> 00:45:00,760
appear in the same fashion.

875
00:45:00,760 --> 00:45:04,020
We've got a methyl
group and a methine.

876
00:45:04,020 --> 00:45:07,260
So, if we look at
the methyl group,

877
00:45:07,260 --> 00:45:10,330
we see that there's one, two
protons next to each other.

878
00:45:10,330 --> 00:45:12,990
So we would expect
the resonance for that

879
00:45:12,990 --> 00:45:16,740
to be split into
three separate peaks.

880
00:45:16,740 --> 00:45:19,440
And there, in fact,
we see a triplet.

881
00:45:19,440 --> 00:45:22,380
And then, for the methylene,
not that it's default now

882
00:45:22,380 --> 00:45:25,500
because there's nothing-- or
that's the only other one,

883
00:45:25,500 --> 00:45:27,570
you would expect one,
two, three, four peaks.

884
00:45:27,570 --> 00:45:28,950
And you see that.

885
00:45:28,950 --> 00:45:31,510
And now this is tricky.

886
00:45:31,510 --> 00:45:35,350
Why do you not get
three peaks for the OH,

887
00:45:35,350 --> 00:45:39,104
even though it's got
two protons next to it?

888
00:45:39,104 --> 00:45:44,040
OH and NH have
exchangeable protons.

889
00:45:44,040 --> 00:45:47,760
And so the proton
is coming on and off

890
00:45:47,760 --> 00:45:51,990
that molecule in a faster
time period than the NMR

891
00:45:51,990 --> 00:45:52,560
measurement.

892
00:45:52,560 --> 00:45:58,380
So you just see an average
of the chemical shifts,

893
00:45:58,380 --> 00:46:00,510
meaning it gives
you a single peak,

894
00:46:00,510 --> 00:46:04,170
rather than splitting
into a triplet.

895
00:46:04,170 --> 00:46:06,420
These didn't come out
very big, but it's just

896
00:46:06,420 --> 00:46:09,570
showing you, with bigger
molecules, you get more peaks.

897
00:46:09,570 --> 00:46:12,150
If you zoom in on these,
you'll see that a lot of these

898
00:46:12,150 --> 00:46:15,810
do not give simple triplets
or quartets or doublets,

899
00:46:15,810 --> 00:46:19,770
that you've got a lot of more
complex splitting going on

900
00:46:19,770 --> 00:46:21,140
in the molecule.

901
00:46:25,140 --> 00:46:28,070
And so here's an
example of an ester.

902
00:46:28,070 --> 00:46:32,300
I think that you all are going
to be synthesizing esters.

903
00:46:32,300 --> 00:46:34,985
So, if we look at
these two compounds--

904
00:46:34,985 --> 00:46:36,360
and something I
didn't point out,

905
00:46:36,360 --> 00:46:39,260
well, I'll show you
this in another slide--

906
00:46:39,260 --> 00:46:42,200
anything that appears
in an aromatic ring

907
00:46:42,200 --> 00:46:44,270
is going to be deshielded.

908
00:46:44,270 --> 00:46:46,130
So it's going to
be far downfield.

909
00:46:46,130 --> 00:46:47,480
And I think I said that before.

910
00:46:47,480 --> 00:46:51,770
You've got the electron
density of the pi orbitals

911
00:46:51,770 --> 00:46:55,110
above and below the ring,
which would shield something.

912
00:46:55,110 --> 00:46:57,800
But those protons are held
not there, but straight out

913
00:46:57,800 --> 00:46:58,410
from the ring.

914
00:46:58,410 --> 00:47:00,500
So they're in a
deshielded region.

915
00:47:00,500 --> 00:47:02,240
So, right off the
bat, we can look,

916
00:47:02,240 --> 00:47:05,630
and we can say, OK, we
know that this must be--

917
00:47:05,630 --> 00:47:11,630
or these peaks must be from the
protons on the phenyl rings.

918
00:47:11,630 --> 00:47:13,880
Unfortunately, there's no
integration on here, but you

919
00:47:13,880 --> 00:47:16,160
also, if I had the
integration values,

920
00:47:16,160 --> 00:47:18,560
you would see that those
both integrate to 5.

921
00:47:18,560 --> 00:47:21,200
And that would tell you
something about it too.

922
00:47:21,200 --> 00:47:25,050
So now the question
becomes, which

923
00:47:25,050 --> 00:47:27,570
splitting patterns
in this region

924
00:47:27,570 --> 00:47:33,330
down here agree with
what we see up here?

925
00:47:33,330 --> 00:47:36,590
So, if we look at
our ester, we see

926
00:47:36,590 --> 00:47:41,090
that, on this ester
over here, we've got--

927
00:47:41,090 --> 00:47:42,710
and we saw this ethyl acetate.

928
00:47:42,710 --> 00:47:47,520
We have the methyl and the
methylene bound to the oxygen.

929
00:47:47,520 --> 00:47:50,780
So we know that the
methyl and the methylene

930
00:47:50,780 --> 00:47:55,340
are going to split into
a triplet and a quartet.

931
00:47:55,340 --> 00:47:58,580
And we know that
that quartet is going

932
00:47:58,580 --> 00:48:03,810
to be shifted downfield because
it's bound to that oxygen.

933
00:48:03,810 --> 00:48:06,080
Now, that's not to say
that also, in this one,

934
00:48:06,080 --> 00:48:09,360
they're not going to be split
into a triplet and a quartet.

935
00:48:09,360 --> 00:48:12,110
But this carbonyl
carbon is not going

936
00:48:12,110 --> 00:48:17,130
to drag the peak as far
downfield as it does over here.

937
00:48:17,130 --> 00:48:24,810
So we can say that this
compound here is from this one.

938
00:48:24,810 --> 00:48:28,020
And this peak right here
is my single methylene

939
00:48:28,020 --> 00:48:30,180
that doesn't have any
protons next to it,

940
00:48:30,180 --> 00:48:35,448
whereas this compound over
here is this one here.

941
00:48:35,448 --> 00:48:36,240
Did I just do that?

942
00:48:36,240 --> 00:48:38,370
No, I just said that backwards.

943
00:48:38,370 --> 00:48:41,890
This compound here is this one.

944
00:48:41,890 --> 00:48:43,810
This compound here is this one.

945
00:48:43,810 --> 00:48:47,560
So here's the single
methylene, and here it is.

946
00:48:47,560 --> 00:48:50,280
Here's the methylene that's
split into a quartet.

947
00:48:50,280 --> 00:48:54,100
And it's right there,
whereas, on this one,

948
00:48:54,100 --> 00:48:56,490
this methylene is shifted
a little farther downfield

949
00:48:56,490 --> 00:48:59,040
because now it's
bound to the oxygen.

950
00:48:59,040 --> 00:49:02,190
Does that make
sense to everybody?

951
00:49:02,190 --> 00:49:02,690
OK.

952
00:49:08,170 --> 00:49:10,810
I'm not going to go
over this completely.

953
00:49:10,810 --> 00:49:11,840
You can look at this.

954
00:49:11,840 --> 00:49:13,960
You can also look up--
you can find stuff

955
00:49:13,960 --> 00:49:15,440
like this online everywhere.

956
00:49:15,440 --> 00:49:18,130
This is a fellow
over in England who

957
00:49:18,130 --> 00:49:21,130
puts out these graphics
called Compound Chem.

958
00:49:21,130 --> 00:49:23,200
I don't know if anybody
follows him on Twitter,

959
00:49:23,200 --> 00:49:27,170
but he's got all sorts of great
chemistry education graphics.

960
00:49:27,170 --> 00:49:29,230
This is one that just
gives you an idea

961
00:49:29,230 --> 00:49:32,710
of the different chemical shift
values and where things appear.

962
00:49:32,710 --> 00:49:35,650
And so you can see an
OH on a carboxylic acid

963
00:49:35,650 --> 00:49:38,440
is going to be very deshielded.

964
00:49:38,440 --> 00:49:42,350
Amide protons are going to be
in this region and et cetera.

965
00:49:42,350 --> 00:49:44,470
So that I can give
you some idea of where

966
00:49:44,470 --> 00:49:46,210
to look for resonances.

967
00:49:50,830 --> 00:49:54,700
I said that we can
take spectra of carbon.

968
00:49:54,700 --> 00:49:57,970
Carbon is a lot less
sensitive than proton.

969
00:49:57,970 --> 00:50:01,120
In fact, sensitivity-wise,
if you just

970
00:50:01,120 --> 00:50:05,590
compare the gyromagnetic
ratio of carbon to proton,

971
00:50:05,590 --> 00:50:07,810
it's a fourth of proton.

972
00:50:07,810 --> 00:50:11,740
So, like I said, we
specify our magnets

973
00:50:11,740 --> 00:50:15,040
by the precession
frequency of protons.

974
00:50:15,040 --> 00:50:17,740
So, on a 500-megahertz
instrument,

975
00:50:17,740 --> 00:50:22,210
it would be a 125-megahertz
carbon instrument.

976
00:50:22,210 --> 00:50:25,630
So you take that one
fourth of a hit because

977
00:50:25,630 --> 00:50:28,390
of the gyromagnetic
ratio, but then

978
00:50:28,390 --> 00:50:32,230
you also take a big
hit because only 1.1%

979
00:50:32,230 --> 00:50:35,020
of the carbon present
in your sample

980
00:50:35,020 --> 00:50:39,100
is made of carbon-13, which
is the NMR-active carbon.

981
00:50:39,100 --> 00:50:43,060
The rest of it is carbon-12,
which is NMR inactive.

982
00:50:43,060 --> 00:50:46,960
But you can still
acquire carbon spectrum.

983
00:50:46,960 --> 00:50:50,920
A carbon spectra has a much
bigger frequency spread.

984
00:50:50,920 --> 00:50:53,440
So you don't have
overlap as much.

985
00:50:53,440 --> 00:50:55,780
That can be very useful.

986
00:50:55,780 --> 00:51:01,030
And this combined with
a proton can tell you

987
00:51:01,030 --> 00:51:02,890
a lot about your molecule.

988
00:51:02,890 --> 00:51:05,650
You're not going to acquire
these on the benchtop

989
00:51:05,650 --> 00:51:06,160
instrument.

990
00:51:06,160 --> 00:51:08,050
Although, I guess
it probably will

991
00:51:08,050 --> 00:51:10,390
if you have a very, very
concentrated sample.

992
00:51:15,790 --> 00:51:18,100
This is just to show an example.

993
00:51:18,100 --> 00:51:21,285
You can do very complex
samples or experiments.

994
00:51:21,285 --> 00:51:24,260
So this is a three-dimensional
spectrum of a protein.

995
00:51:24,260 --> 00:51:26,740
So this is something you would
use in determining a protein

996
00:51:26,740 --> 00:51:28,630
structure.

997
00:51:28,630 --> 00:51:30,300
I've never acquired
one of these.

998
00:51:30,300 --> 00:51:33,250
So all I can tell
you is that you're

999
00:51:33,250 --> 00:51:36,490
looking both at carbon
resonance-- what

1000
00:51:36,490 --> 00:51:37,490
do we have up here?

1001
00:51:37,490 --> 00:51:38,500
Oh OK, sorry.

1002
00:51:38,500 --> 00:51:41,140
So it's the protein
was expressed

1003
00:51:41,140 --> 00:51:46,300
by bacteria that were growing in
food that was labeled with N-15

1004
00:51:46,300 --> 00:51:50,740
and C-13 so that
there's incorporation

1005
00:51:50,740 --> 00:51:52,210
of those nuclei in there.

1006
00:51:52,210 --> 00:51:55,940
And it will give you a
signal, and you can use that.

1007
00:51:55,940 --> 00:51:56,440
Let's see.

1008
00:51:56,440 --> 00:51:59,840
I'm almost finished, but I
think we're about out of time.

1009
00:51:59,840 --> 00:52:03,530
Sample preparation, when
you're preparing your samples,

1010
00:52:03,530 --> 00:52:08,150
it is important to
prepare clean samples.

1011
00:52:08,150 --> 00:52:11,700
There should not be particulate
matter in your samples.

1012
00:52:11,700 --> 00:52:16,220
You should filter them if you
do have particulate matter

1013
00:52:16,220 --> 00:52:18,830
from your reaction
because that will--

1014
00:52:18,830 --> 00:52:23,060
having particles in there will
lead to poorer spectra that

1015
00:52:23,060 --> 00:52:26,300
will be difficult to interpret.

1016
00:52:26,300 --> 00:52:29,360
NMR are the very thin,
glass-walled tubes.

1017
00:52:29,360 --> 00:52:31,660
So be careful with them.

1018
00:52:31,660 --> 00:52:34,980
If you snap this, you can
easily stick it in your hand.

1019
00:52:34,980 --> 00:52:37,660
So be very careful with that.

1020
00:52:37,660 --> 00:52:41,390
Use a deuterated solvent when
you're preparing your samples.

1021
00:52:41,390 --> 00:52:44,030
I think you will be given
that by your TAs anyways.

1022
00:52:44,030 --> 00:52:46,430
And never put a dirty
tube in the instrument.

1023
00:52:46,430 --> 00:52:50,780
You should always clean the
tube off on the outside.

1024
00:52:50,780 --> 00:52:55,940
And then I think the last slide
that I have is about shimming.

1025
00:52:55,940 --> 00:52:58,400
Shimming is adjusting
the homogeneity

1026
00:52:58,400 --> 00:53:00,180
of the magnetic field.

1027
00:53:00,180 --> 00:53:03,990
So, if you remember
from that equation--

1028
00:53:03,990 --> 00:53:08,670
and you don't even have to
know how to solve this--

1029
00:53:08,670 --> 00:53:15,980
so your frequency is
directly proportional

1030
00:53:15,980 --> 00:53:18,880
to the magnetic field strength.

1031
00:53:18,880 --> 00:53:22,900
Shimming means making your
magnetic field homogeneous

1032
00:53:22,900 --> 00:53:27,940
so that the top of your sample
feels the same strength field

1033
00:53:27,940 --> 00:53:30,010
as the bottom of your sample.

1034
00:53:30,010 --> 00:53:32,950
The machine will do
it automatically,

1035
00:53:32,950 --> 00:53:35,560
but, if the top of
your sample feels

1036
00:53:35,560 --> 00:53:38,170
a different magnetic field
strength than the bottom,

1037
00:53:38,170 --> 00:53:41,320
then it's going to have two
separate frequencies for where

1038
00:53:41,320 --> 00:53:45,040
those protons precess, which
means the line broadens out.

1039
00:53:45,040 --> 00:53:46,810
And, if that line
broadens out, it

1040
00:53:46,810 --> 00:53:50,140
makes it harder to interpret.

1041
00:53:50,140 --> 00:53:53,960
And then I'll skip
over this one.

1042
00:53:53,960 --> 00:53:56,240
The last thing, I
guess, questions, I

1043
00:53:56,240 --> 00:53:58,670
put in some references in here.

1044
00:53:58,670 --> 00:54:01,040
This is a great thing
to do with old magnets.

1045
00:54:01,040 --> 00:54:03,110
If you're artistic
with cutting tools,

1046
00:54:03,110 --> 00:54:06,710
I would love to have my own
pizza oven with an old magnet.

1047
00:54:06,710 --> 00:54:09,130
So, if anybody has any
questions, please let me know.

1048
00:54:09,130 --> 00:54:10,338
AUDIENCE: Pretty cool lesson.

1049
00:54:14,660 --> 00:54:17,150
JOHN GRIMES: And no, that's
not a friend of mine's either.

1050
00:54:17,150 --> 00:54:20,664
I just snagged that off the web.

1051
00:54:20,664 --> 00:54:22,530
AUDIENCE: That's hilarious.

1052
00:54:22,530 --> 00:54:23,850
JOHN GRIMES: Anything else?

1053
00:54:23,850 --> 00:54:24,350
Thank you.

1054
00:54:24,350 --> 00:54:25,637
[APPLAUSE]

1055
00:54:25,637 --> 00:54:27,720
And, if you want to look
at this if you have time,

1056
00:54:27,720 --> 00:54:29,530
you can come up.