INFRARED SPECTROSCOPY to find the functional group

INFRARED SPECTROSCOPY

1. SEMINAR
ON
INFRARED SPECTROSCOPY
SUBMITTED BY:
KUNUMUNU SWAIN
ROLL NO:25602

2. Introduction
Principle
Theory
Instrument
Sample preparation
Qualitative &quantitative
Analysis
Use
Application
Limitation
conclusion

3. INTRODUCTION
Subset of spectroscopy that deals with infrared
region of spectroscopy.
Used to identify functional group of compounds
and sample composition.
Instrument used for analysis is infrared
spectrometer.
This technique is a popular tool for structural
elucidation and compound identification.

4. ELECTROMAGNETIC RADIATION
It is a form of energy which is propagated at the speed of light in
vacuum as oscillating waves where electric field & magnetic field
are perpendicular to each other
Used to see very small objects. It obeys the relation
E = hν=hc / λ.
INFRARED RADIATION:
It is a section of electromagnetic radiation having
wavelength = 0.8 to 1000µm
wave number = 14000 to 10cm
-1
frequency = 1 x10
11
to 4000 x 10
11
Hz
Infrared region is divided into 3 sections. Those are :-
near IR, mid IR, far IR.

5. CONTINUE…..
Near IR Mid IR Far IR
Wave number 14,000–4,000 4,000–400 400–10
(in cm
-1
)
Wavelength 0.78–2.5 2.5–50 50–1,000
(in μm)
SPECTROSCOPY:-
Seeing the unseeable.
It is the study of interaction between radiation and matter as a
function of wavelength.
A Plot of response for energy as a function of wavelength or
frequency is referred to as spectrum.

6. PRINCIPLE
If the frequency of the radiation matches the vibrational
frequency of the molecule then radiation will be absorbed,
causing a change in the amplitude of molecular vibration.
The infrared spectrum of a sample is recorded by passing a beam
of infrared light through the sample.
Examination of the transmitted light reveals how much energy
was absorbed at each wavelength. From this, a transmittance or
absorbance spectrum can be produced, showing at which IR
wavelengths the sample absorbs. Analysis of these absorption
characteristics reveals details about the molecular structure of the
sample.

7. THEORY
Vibrational mode in a molecule to be "IR active," it must be associated with
changes in the permanent dipole.
Linear molecules have 3N-5 degrees of vibrational modes whereas nonlinear
molecules have 3N-6 degrees of vibrational modes.
More complex molecules have many bonds, and their vibrational spectra are
correspondingly more complex, For example a CH
2group, commonly found in
organic compounds can vibrate in two different way:
Stretching: symmetrical stretching
antisymmetrical stretching
Bending: scissoring
rocking
wagging Stretching > Bending > Wagging/Twisting
twisting:

9. INSTRUMENTS
Two types of spectrometers are used. Those are:
Dispersive spectrometer
Fourier transform spectrometers.
Dispersive spectrometer
SOURCE:-Nernst glower , Globar, Nichromecoil.
MONOCHROMATOR:-
It disperses a broad spectrum of radiation. Prisms or gratings are with
variable-slit mechanisms. Narrower slits resulting in better resolution.
Wider slits allow more light to reach the detector and provide better system
sensitivity.
DETECTOR:-
Two types of detectors are used; thermal detectors and photon detectors.
Thermal detectors include thermocouples, thermistorsand pneumatic
devices. Photon detectors rely on the interaction of IR radiation and a
semiconductor material.

10. FIG: Dispersive spectrometer

11. FOURIER TRANSFORM INFRARED
SPECTROMETER
COMPONENTS:-
SOURCE:-Nernst glower ,Globar and Nichrome coil..
INTERFEROMETER:
The most commonly used interferometer is a Michelson interferometer. It
consists of three active components: a moving mirror, a fixed mirror, and a
beam splitter .The two mirrors are perpendicular to each other.
At the beam splitter, half the IR beam is transmitted to the fixed mirror and
the remaining half is reflected to the moving mirror. After reflection from the
two mirrors, they are recombined at the beam splitter. Due to change in the
relative position of the moving mirror to the fixed mirror, an interference
pattern is generated. The resulting beam then passes through the sample and
focused on the detector.
DETECTOR:
The two most popular detectors for a FTIR spectrometer are deuterated
triglycine sulfate (DTGS) and mercury cadmium telluride (MCT) .

13. ADVANTAGES OF FTIR OVER
DISPERSIVE SPECTROMETER
1.Better speed and sensitivity .
2.The beam area of an FT instrument is usually 75 to 100 times larger than
the slit width of a dispersive spectrometer. Thus, more radiation energy is
made available. This constitutes a major advantage for many samples or
sampling techniques that is energy-limited.
3.The use of a helium neon laser as the internal Reference in many FTIR
systems provides an automatic calibration in an accuracy of better than
0.01 cm
–1
.
4.Simpler mechanical design. There is only one moving part, the moving
mirror, resulting in less wear and better reliability.

14. SAMPLE PREPARATION
GAS:-
Gaseous samples -sample cell with path length 5-10cm & pressure of 50 torr.
LIQUID:-
oCarbon tetrachloride for 4000 -1330 cm
–1
and carbon disulfide for 1330 -625
cm
–1
region.
oSmearing Sample: A drop of sample is squeezed between 2 salt plates of NaCl
held together by capillary attraction to form a film of 0.01mm thickness.
SOLID:-
oThe sample (1 to 5 mg) is ground with a mulling agent (usually Nujol) of 1
to 2 drops. This mull is pressed between two IR-transmitting plates .
oPellets are made from the sample (0.5 to 1.0 mg) i.e.finely ground and
intimately mixed with approximately 100 mg of dry potassium bromide
powder.
o“Cast film" technique is used mainly for polymeric materials. The sample is
first dissolved in a suitable, non hygroscopic solvent, a drop of which is
deposited on surface of KBr or NaCl cell & is then evaporated to dryness

15. QUALITATIVE ANALYSIS
Structural Elucidation:
Energy follows vibration frequency of atoms
Light atoms vibrate more rapidly –CH, NH, OH vibrations > 2800 cm-1
Multiple bonds vibrate more rapidly than
Triple bonds C ΞC (2100-2200) C ΞN (2240-2280)
Double bonds C=O (1680-1750) C=C (1620-1680)
Single bonds C–O (1025-1200)
Compound Identification:
Since the IR spectrum of every molecule is unique, one of the most positive
identification methods of an organic compound is to find a reference IR
spectrum that matches that of the unknown compound.
Reference spectra are available in printed and electronic formats &
Computerized search programs can facilitate the matching process.

18. QUANTITATIVE ANALYSIS
For a single compound system:-
The absorbance at any frequency is expressed as
A= abc a = absorptivity
b = path length
c = concentration
For Complex Mixtures:-
Matrix method:
The K-matrix method, where Beer's law becomes:
A = kc as k = a xb
Assuming Beer's law is additive, Above equation can be written in matrix
form for 1 to n components as:
A = KC
Curve fitting:
It is used When the spectrum of a mixture is known to consist of specific
pure components, and spectra of these components are available, it should be
possible to generate a linear combination of the pure component spectra that
reproduces the spectrum of the mixture.

19. USE & APPLICATION
Identification of all types of organic and many types of inorganic
compounds
Determination of functional groups in organic materials.
Identification of compounds by matching spectrum of unknown
compound with reference spectrum (fingerprinting).
Identification of reaction components and kinetic studies of
reactions .
Identification of molecular orientation in polymer films ,
measuring the degree of polymerizationin polymer manufacture
Identification of plastics, and resins
Widely used in research and industry.

20. LIMITATION
General
• Minimal elemental information is given for most samples.
• Background solvent or solid matrix must be relatively
transparent in the spectral region of interest.
• Molecule must be active in the IR region. (When exposed to IR
radiation, a minimum of one vibrational motion must alter the
net dipole moment of the molecule in order for absorption to be
observed.)
Accuracy
In analysis of mixtures under favourable conditions, accuracy
is greater than 1%. In routine analyses, it is ±5%.

21. CONCLUSION
Infraredspectroscopyisanabsorptiontechniquedealswiththe
infraredregionofelectromagneticspectrum.
Therearetwotypesofinstrumentsusedininfrared
spectroscopy.ThosearedispersionspectrometerandFourier
TransformInfraRedspectrometer.
Theinfraredspectroscopytechniquehasawidevarietyof
application.Itismainlyusedtodeterminethestructureofthe
moleculeandthetypeofthebondinit.Itdeterminesthetype
offunctionalgroupinorganic&inorganiccompounds.Itis
widelyusedinbothresearchandindustryasasimplereliable
techniqueformeasurement,qualitycontrol&dynamic
measurement

22. REFERENCE
ASM Metal Handbook , Volume-10, Material Characterisation.
Principle Of Instrumental Analysis By Douglas & Donald.
P.R. Griffiths, Chemical Infrared Fourier Transform
Spectroscopy, John Wiley & Sons.
M.P. Fuller and P.R. Griffiths, Appl. Spectrosc., Vol 34
P. Kubelka and F. Munk, Z. Tech. Phys., Vol 12
P.R. Griffiths, in Fourier Transform Infrared Spectroscopy,
Applications to Chemical Systems, Vol I,
www.infrared spectroscopy.com
www.infraredanalysis.com