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8/10/2019 Spectro Copy

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Spectroscopy

Introduction: In this chapter we are

going to consider how the differenttypes of radiation affect molecules

and how this relation can be used.


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Electromagnetic spectrum

Unlike water waves oscillations of

electromagnetic waves involve not matter

but electric and magnetic field.


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Electromagnetic spectrum


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Electromagnetic Spectrum

Ethanoic acid can be produced in the wine

due to the oxidation of wine. In the spectrum

of ethanoic acid there is a large peak

labelled X at about 1700 cm-1 thiscorresponds to the C = O bond stretching.

There is no such bond in ethanol so

chemists can check the extent of anyoxidation by monitoring the growth of this

peak.


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Due to the electromagnetic field

inside the microwaves water

molecules in the food to line up with

the field. The field then switches tothe opposite direction and the water

molecules swivel round to line up

again. This causes the energy in themicrowaves to be converted into

thermal energy and this heats the

food. This happens only in polar


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Using microwaves organic

compounds which are soluble in both

an organic solvent and water can be

separated as organic solvent is notaffected by microwaves.

Due to ultraviolet radiationoxygen

molecules to dissociate into reactiveoxygen atoms by homolytic fission. This

can react with other oxygen molecules to

produce ozone.


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Using the technique of ultraviolet

radiation, scientists have studied

organic molecules, polymers,

nanoparticles and semiconductors.

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High resolution nmr

spectroscopy

When atoms like hydrogen are placed

in a magnetic field, the nuclei align

themselves with the field, just as a

bar magnet aligns itself with the

Earthsmagnetic field.

Hi h l ti


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High resolution nmr

spectroscopy

Fig.: the energy difference between these two

states corresponds to radio frequencies, according

to the relationship E= hf


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High resolution nmr

spectroscopy

The nuclei of atoms can be

pushedfrom one alignment

to the other by the energy

from radio waves.


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High resolution nmr

spectroscopy

The spectrum of

frequencies absorbed by a

particular molecule provides

a great deal of information

about the position of thehydrogen atoms in it.


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High resolution nmr

spectroscopy

The hydrogen atoms in a

molecule that is subjected to

an externally applied

magnetic field do not all

experience the samemagnetic field. This is

because the proton in the


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High resolution nmr

spectroscopy

nucleus of a hydrogen atom is

shielded by electrons close to it.

The frequency at whichmagnetic resonance occurs is

an indication of the chemicalenvironment of a proton within a

molecule.


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Low resolution nmr

spectroscopy


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Low resolution nmr

spectroscopy

Low resolution nmrenables the

identification of:

The number of different types ofproton from the number of

peaks

The relative number of hydrogen

atoms in each group from the

area under the peaks.


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High resolution nmr

spectroscopy

High resolution of the spectrum

splits the signals into multiplets.

The splitting occurs because ofthe interaction between protons

on neighbouring atoms. This

interaction is called coupling andcauses the splitting into distinct

lines.


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High resolution nmr

spectroscopy

Fig.: High resolution spectrum of ethanol


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High resolution nmr

spectroscopy

The number of lines in the

split pattern for a peak is

equal to one more than the

number of hydrogen atoms

in the adjacent group in themolecule.


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Use of nmr spectroscopy in

practical field

Nuclear magnetic resonance

and other methods of

structural determination enablechemists to determine

chemical structure veryquickly.


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practical field

Nuclear magnetic resonance and other

methods of structural determination

enable chemists to determine chemical

structure very quickly.

nmr spectroscopy technique can be

used to determine the molecular

structure of organic compounds by

studying the series of peaks in the

spectrum.


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practical field

nmr imaging is an extremely rich

source of information about what is

going on inside patients. A process known as diffusion

weighted imaging produces as nmr

image which allows very specificdiagnosis of the area of damage after

a stroke.


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practical field

Nicotine is made in pharmaceiticles

which may contain a chemical cotinine,

which has a very similar structure to

nicotine but has undesirable properties.

Nmr spectroscopy can measure the

purity of samples quickly and

accurately, so that if cotinine appears in

a batch of the drug it can be isolated

and removed before the nicotine is used

therapeutically.


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Mass Spectroscopy

Nicotine is made in pharmaceiticles

which may contain a chemical cotinine,

which has a very similar structure to

nicotine but has undesirable properties.

Nmr spectroscopy can measure the

purity of samples quickly and

accurately, so that if cotinine appears in

a batch of the drug it can be isolated

and removed before the nicotine is used

therapeutically

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