come back friends welcome to another
video tutorial from shamans biology in
this video lecture we'll be talking
about IR spectroscopy which is also
known as infrared spectroscopy you know
infrared is belonging to our normal
electromagnetic wavelength if you look
at the wavelength it is a large
wavelength it's much bigger than the
visible wavelength that we can see so
that is why we can't see infrared but
this infrared light can be very
beneficial for understanding the
structure of different chemical
compounds especially the structure of
different groups or chemical groups of
those molecules so I asked spectroscopy
is also known as vibrational
spectroscopy or the chemical group or
group related spectroscopy now what does
that mean
ir spectroscopy depends on or it
actually helps us to find out the
structure of different chemical groups
that are present in a molecule mostly
the functional group and the presence of
functional group can be very well
detected with the help of IR
spectroscopy for understanding the
structure of unknown chemical compounds
we have different techniques we have NMR
spectroscopy we have x-ray
crystallography we have mass
spectrometry but this one this IR
spectroscopy is not that powerful to
give you an data about the whole
chemical compound but it is good enough
to give you idea about the functional
group that are associated with the
target molecule that you are
experimenting with so let us go into it
in IR spectroscopy works in a very
simple principle and that principle is
the bond between the different atoms the
atoms that are present in a chemical
compound their bond or link with each
other
either with a single bond or double bond
or even triple bond
so those molecules can have saturation
or on saturation or the whole process it
depends on how those bonds are behaving
because if you look at the bond
if you look at the chemical compound and
atoms are linked with bonds those bonds
are not permanent it is not fixed
they are always involving with different
type of motions that could be vibrations
then-known add those bond vibrations the
vibration means let me give a simple
example if we are talking about a carbon
attached with a hydrogen for example oh
it's a carbon it has to be a nitrogen or
oxygen for example that that interaction
it could be with a single bond or it
could be the interaction with a double
bond but in any sense you can imagine
that this two atoms they are linked with
not a simple line you can think of it as
a as a supreme so that means if you
imagine this is attached sorry it's
attached like a touch with a spring with
an oxygen so now you think this spring
can go from each other towards each
other or it can come towards each other
like that so the spring can be like
dragged opposite to each other now
sometimes can be towards each other so
by this fashion what we can see some
oscillation you can see this sort of
oscillation there is no known as wagging
that is not that is not wagging that's
kind of a stretching we can say it is
known as stretching so this bond they
can have a stretching effect if you can
take it away from each other and I also
bring them close to each other just like
a spring in - stretching is always going
on in all those bonds there is also
another effect known as waggly what is
that for understanding that let's take
one compound as an example and that is
let us say formaldehyde formaldehyde if
you take this is the structure of
formaldehyde where carbon is attached to
this oxygen this is the carbonyl carbon
because it is a carbonyl group that we
can see here this carbonyl group if we
talk about this particular carbonyl bond
forget about the hydrogen's here this
particular carbon in bond if you look at
here
just imagine the carbon is attached to
the oxygen with a spring so there is a
stretching effect so they have a
stretching effect between this carbon
and oxygen this stretch like this over
here and also there is another effect
that let us consider this as oxygen is
attached to the carbon and just like
like this it can also rotate in a zigzag
fashion like that this is known as
wagging this head is moving like this so
this is the wagging movement like that
so we have wagging and we have
stretching here two type of effects that
we can always see so in this chemical
compound you will see always this
stretching and wagging going on now
there is a frequency by which the
stretching continues and the wagging
continues normally in case of this
formaldehyde the stretching is 2 Hertz
and the wagging is considered as 4 Hertz
for example say Hertz is the frequency
with which this stretching or wagging is
taking place for the stretching the
frequency is 2 Hertz for the wagging the
frequencies 4 Hertz
for example now what we see here for
this compound this type of rotation and
vibrations around the bonds are very
important for giving us the idea about
the type of functional group we are
looking at whether the functional group
is carbonyl carbonate attached or it
could be like any other type of bonds
attached with it there are different
types of signature movement and
signature vibration and stretching for
different types of bonds if it is a
double bond there is a kind of
stretching if it is a single bond a
different way of stretching if it is a
triple bond that's another different
kind of stretching so those variations
among those chemical compounds are going
to give us so many different varieties
of data which will help us to find out
what kind of compounds we are talking
about because I told you our job for IR
spectroscopy is to find out
a target group functional group that is
what we need to find out now what
exactly I our spectrometer does let us
look at here let us take this compound
as an example and what we do here in the
IR spectrometer that we simply put
infrared radiation let us say this is
the gun infrared this is from this is
where the infrared comes in we simply
write it as a light source because it is
light source just we cannot see it
because it is having a longer wavelength
over there and also the wave number is
also little big here so this infrared
radiation this light source is coming in
and this is the chemical molecule
present here so let me draw the chemical
molecule like that now we can control
the frequency of this infrared light
that is hitting this compound let us say
this I R is moving in a frequency of 1
Hertz now we know that in this compound
the vibrations and the stretching and
wagging all this movements are none of
them are 1 Hertz the stretching is 2
Hertz wagging is for Hertz
so as this IR is hitting this molecule
in 1 Hertz frequency it is not going to
influence this molecule so this compound
is not going to observe any of that so
it is going to emit all of it this is
the idea
ir is hitting it 1 Hertz there is
nothing going on in the 1 hertz
frequency in this molecule no bond
expression in the 1 Hertz so all of this
light that is passing through the
molecule it is completely passed none of
the light is observed so at the end of
this at the end of this chamber we have
the detector we always have detector at
the end Big D
it stands for detector so detector
detects 100% lights to be emitted
none of them are observed so now once
detector detects that detected is
connected with the computer and that is
also connected to the monitor screen
where we can see a graph for me now if I
do the graph how it will look like it
will look something like
if I do the graph like this in the
x-axis we are talking here about the the
percent immittance or the percent
immittance that is the percent emission
and this is in the sorry this is in the
y axis in the x axis we have the wave
number which is in inverse centimeter
and we can we can guess it from like say
here is a 4000 at this point to let us
say here is a 500 inverse centimeter
okay so this is the idea and here we
have the hundred person technician at
the top and at the very beginning this
is zero percent emission so this is the
emission scale so what we can see here
as all of this light is passed
none of them observed so we see 100%
emission here at the very beginning with
one Hertz let us say for for this
understanding we simply do this
calculation in Hertz the frequency we
are talking about so at 1 Hertz we see
hundred percent emission okay now let us
say let us change this frequency of IR
light that is going in now let us say
the frequency we go with 2 Hertz what
will happen we know that this C and O
this double bond the stretch in the
frequency of 2 Hertz and they wag in the
frequency of 4 Hertz right so as the
frequency of this I are hitting this
molecule matches with the frequency of
the stretching between the carbonyl
carbon and oxygen that is also 2 Hertz
this compound will observe most of the
light most of the IR spectrum most of
this light is will be observed by this
formaldehyde there and very little will
pass very very little theoretically it
should observe all the light because it
will give the energy source and will
start stretching itself but sometimes
you know due to the
practical experiences you can see that
some part of this UV radiation is also
passed to the detector but detector
detects very very less amount which acts
as a background noise we can tell so for
the two herds if you look at here for
the second two words you will see shard
drop you see a drop in the emission now
let's go back to the three Hertz if we
know I mean the three Hertz again none
of them none of this compound they have
a three Hertz frequency in anything so
again they are not going to observe
three hours they are going to leave it
away so most of the light will be
emitted so again in three nerds you will
find a steady you have 100% emission now
finally it goes with the four Hertz once
it again fires it in the four Hertz the
frequency of the IR radiation is four
Hertz is again to inspire the wagging
movement so most of it will be observed
very few will be emitted act as a
background noise in that case also we
will see a drop four Hertz
so by this fashion what we can see in
this graph this kind of graph you will
see it's very common type of graph or IR
spectra you see lot of things down like
normally it 100% immittance but then you
will see the absorbance this drop in the
immittance means absorbance that's what
we are talking about absorbance whenever
absorbance that means this molecular
compound that we are testing is
observing the IR and that specific
frequency that matches the frequency of
stretching and wagging or the vibration
of that functional group now this
vibration of the functional groups are
specific for specific functional groups
for this carbonyl this will be fixed to
Hertz for this stretching for hurts for
wagging now remember it also varies with
the situation of this molecule
how other groups are placed it's not
that simple here we draw a very simple
example multiple groups are present and
it will have influence for the presence
of other groups as well and secondly it
also depends on the length between the
bonds that are present between the two
components here which is in this case
carbon and oxygen as it's a
double-stranded bond and also if it is a
double bond the the stretching movement
and vibration would be different the
frequency of vibration will also be
different if it's a single bond if it is
a triple bond it will be also changed so
based on the number of bonds it will
also vary the length of the bound it
will also vary so all these things
matters a lot and also the presence of
other groups also determine what kind of
absorbance it will actually have so that
in a sense of whole process so now if
you look at some of these graphs you
will see hundred percent emitters and in
the in the x-axis you will probably find
a lot of data like in the wave number
the data in the wave number means it
will be like centimeter inverse value of
the wave number and you will see like
four thousand here and five hundred here
so this is going to give you an idea
about then the the re it's not about
we're not talking here about like let's
say let me just it is that let me talk
about it is this one let's say we're
talking about the graph and the data
about the wave wave number for the
infrared and whenever we are talking
here the four thousand and here we have
let's say 500 only and here we see the
different emission in the in the y axis
so what we see here if you look at very
carefully you will see a lot of lot of
different Peaks coming in going down
like lake peaks like this and at the end
after a specific point you will see
something like that what is that I am
going to explain in a moment there are
two segments you can form by looking at
any of this
ir spectra data one it is completely
based on the wave number that we are
looking for for this wavelength the wave
number that we're looking for it belongs
to the it starts from 4000 to 1800 that
range and then another range from 1800
to 500 mostly from 4000 to 1800 that
area of the data it represents it
represents the the functional group
mostly it represents all them all the
specific basics functional group that we
know of in the in the organic chemistry
all those functional group they range
from this 4,000 to 800 but now if you go
from 1700 to 500 that range that is
mostly filled with very tiny
modification among those functional
groups and that is very specific to the
specific molecules so that region of the
spectra is very important and the
resolution is also very very important
at that end of the spectra because that
is known as the fingerprint region this
first area is known as a functional
group region because it will give you
the idea about the functional group of
the chemical compound which will be very
important idea but the second one will
give you the idea about the exact type
of functional group you are talking
about it is going to give you the idea
about the exact atom present near each
other that is known as the fingerprint
region because this fingerprint region
why fingerprints are unique for all of
us so fingerprint region means this
region will be unique to all those
different chemical compounds that is the
idea so for getting this if you get a
graph like that and if you get a idea
about the about the functional group and
fingerprint along with those two things
each other it's going to give us the
idea about what kind of chemical
compounds we are talking about and
that's what I are actually do IR
spectroscopy will help us to get the
idea about the molecules different
groups and those the presence of group
will be very beneficial for us to
calculate
what kind of molecule we are talking
about that is all about infrared
spectroscopy I hope you understand this
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