What Is NMR Spectroscopy? - 3.15

Hi. My name Doctor Noazdan. I'm a senior lecturer,

at University of Chester,

and I mainly teach organic chemistry and medicinal chemistry.

Today I'm going to talk to you about the different analytical

techniques you need to use for identification of organic

compounds as there you're a level exam board. So, the first,

analytical technique we are going to talk about is nuclear

magnetic crew resonance. So have you ever wondered how we

as organic chemist,

tend to know the structure of our products because we tend to

do reactions on a daily basis, and sometimes we are,

we cannot actually see our project with eyes, but we need

to find the structure of these molecules.

So we we use different analytical techniques to

identify the structure of smart use. The one we use on

a daily basis is basically the NMR or nuclear magnetic resonance.

Most of not all of the analytical techniques will

depend on the interaction between the atoms and or

between the molecules and the electromagnetic radiation.

So electromagnetic radiation,

have photons, with some energy.

They differ in their energy depending on which region in

the electromagnetic radiation when a molecule or an atom

absorbed the light or absorb photons from a certain region

of electromagnetic radiation with a certain energy that

tends to cause some changes in that molecule or in that atom.

The amount of energy that has been absorbed can be measured

and will give us a signal that will give us some information

about the structure

So let's start by talking about the NMR. So let's

hear this statement and try to analyze it step by step.

So nuclear magnetic resonance spectroscopy

is an instrumental technique based on mentoring how spinning

nuclei with magnetic dipole interact with applied magnetic

fields and absorb radiation.

Probably this sentence doesn't make a lot of sense to you, but let's,

analyze it and explain it. So the first thing we said

that spinning nuclei what are the nuclei?

What are the spinning nuclei? So nuclei,

that have an odd number of

neutrines or basically the total of electrons, of protons

and neutrons will have a spin.

They will tend to spend like a magnet.

But the ones that have an even number, a total even number,

they will not have the spend number. They will not have

aspen like a magnet. So how would we know whether they are hot or even?

Remember that we must number of, an atom,

is basically the total number of,

nutrients and protons inside the nucleus.

So the atoms that have an odd, mass number

are the one will have a span. The one that don't will not

have a span. So these are the ones that we are going to

study. The one with an odd number.

There are only two nuclei or two types of nuclei

that we are going to study for the neutromagnetic resonance,

which are the proton NMR and the Carbon thirteen NMR.

So proton is the hydrogen. So the hydrogen hydrogen one. We

know that the isotope of hydrogen,

this is the most abundant isotope of hydrogen is the hydrogen one.

It only has one brought in. This is why we call hydrogen

one NMR as proton NMR. And the second one is the Carbon thirteen,

so we know the most abundant isotope of Carbon is the Carbon

twelve, but it has an even number of,

mass number or an even number of nutrients and protons, which

twelve, so it doesn't have a spin. Carbon thirteen has an

abundance of around one percent, so it will have a

spin, and it can give us a signal in the, NMR.

So Carbon thirteen and Proton or hydrogen one are the one we

need to study and know about here.

So this is the first thing. This is the spelling nuclei.

So how can we make use of this? So this is spelling nuclei

when without an applied magnetic field,

they were just been in all directions.

So basically imagine that one is creating a small differing one direction.

The other one is creating a medical on the other direction

so they will cancel each other out because they this is random

spin in all directions for all of the nuclei.

So once you bought an external magnetic field, this

nuclei will start to arrange them

into two different positions. The first one,

they will start to spin and align themselves with the

external magnetic field. So they are basically within the same,

the same direction as the external magnetic field.

There are also another

state where they will be aligned opposite to the

external magnetic field.

There's a difference in the energy between these two states

Normally, most of the, nuclei will be arranged with the

external magnetic field because it's lower energy.

Very tiny ones will be arranged to,

opposite to the external magnetic field. But if we

irradiate these nuclei, which are in these, magnetic fields to,

electromagnetic radiation within the radio frequency

range, then the energy of this radio frequency

are just enough to cause the flipping of one state to

another. So basically, this nuclei,

if they absorb enough energy that cover the difference in

the energy between the two, states.

So then the difference in the energy between the two state

they can flip from being arranged with the external

magnetic field to be arranged against the external magnetic

field. And this difference in the energy, this amount of,

of radio frequency that has been absorbed and led to this,

let to this flipping,

can be actually measured and will give us a signal that will

give us some information about the structure of our NMR. So the

NMR,

basically, what we get at the end is that we're gonna get, a

spectrum on the x axis is called the chemical shift. And

we, the chemical shift, we give it the, symbol delta.

We measure it in part per million,

and will give us some signals that we're gonna see these signals.

Each signal will give us some information about our structure

and the y axis is simply the intensity of the signals. So

this is the main theory about how the NMR work and

how we can find the structure of molecules or apply the theory,

of the NMR to find the structure.