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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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Electromagnetic Spectrum
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Electromagnetic Spectrum
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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Electromagnetic Spectrum
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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Electromagnetic Spectrum
Using the technique of ultraviolet
radiation, scientists have studied
organic molecules, polymers,
nanoparticles and semiconductors.
Hi h l ti
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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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Use of nmr spectroscopy in
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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Use of nmr spectroscopy in
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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Use of nmr spectroscopy in
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