Infrared spectroscopy involves using infrared radiation to stimulate molecular vibrations within a sample. The technique provides information about the types of chemical bonds in a molecule based on the frequencies at which they absorb infrared radiation. The summary discusses the main components of an IR spectrometer including the source, monochromator, sample handling techniques, detectors, and applications of IR spectroscopy such as determining functional groups, molecular structure identification, and quality control.

1. Presenter-Presenter-
Naveen KadianNaveen Kadian
1

2.  Introduction
 Principle
 Instrumentation
 Sample Handling
 Interpretation
 Applications
2

3. • What is Spectroscopy?
Technique that uses the interaction of energy from radiations with a sample to perform an
analysis.
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• Terms Associated with IR Spectroscopy-
• Transmittance
• Wave number
• Requirement for IR Spectroscopy-
• Correct Wavelength of Radiation
• Electric Dipole
• Planck Constant
λν hchE ==
IR Spectroscopy:
NEAR INFRARED: 0.8 -2.5 µm, 12500 - 4000 cm-1
MID INFRARED: 2.5 - 25 µm, 4000 - 400 cm-1
FAR INFRARED: 25 - 1000 µm, 400 - 10 cm-1

4. http://upload.wikimedia.org/wikipedia/en/8/8a/Electromagnetic-Spectrum.png
e-
Bond breaking and ionization
Electronic excitation
Vibration
Rotation

5.  Infrared radiation stimulates molecular vibrations
 Types of Molecular Vibrations
› Stretching
› Bending
 In-Plane Deformations
 Out-Plane Deformations
5

6.  Factor effecting Vibrations:
 Fermi Resonance
 Resonance causing the transfer of energy from fundamental to overtone
and vice-versa
 helps in explaining the doublet
 Electronic Effects
 electro+ve +I effect decrease wavenumber
 Electro -ve -I effect increases wavenumber
 Hydrogen Bonding
 stronger the hydrogen bonding greater the absorption shift towards lower
wavenumber
 Intramolecular Bonding give sharp peaks whereas Intermolecular
Bonding give Broad peaks which is concentration dependant
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• Stretching frequencies are higher than corresponding bending frequencies.
• Triple bonds have higher stretching frequencies than corresponding double
bonds, which in turn have higher frequencies than single bonds.

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• Instrumentation of IR Spectrophotometer mainly consists of:
• Source
• Monochromators
• Sample Cells
• Detector
• Sources:
A hot material emits a continuum of radiation. Blackbody (no envelope):
intensity highest near 5000 cm-1
; about 100 times lower near 500 cm-1
.
a. Nichrome coil heated electrically to 1100o
C and a black oxide film forms.
Simple, robust, reliable, long lifetime.

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b) Nernst glower
aux.
heater
2 - 5 cm
Has - temp coefficient.
of resistance.
1 - 3 mm dia.
ceramic holder
Y2O3,
ThO2,
ZrO2
heated up
to 1500oC
Pt leads
cement

9.  Monochromators:
› Prism Monochromators:
 used for the selection of radiation of desired Frequencies
 made up of NaCl due to its high Dispersion in the range of 4 to
15µm
› Grating Monochromators:
 higher dispersion
 mainly of Aluminum
 Sampling Techniques:
› For Solids
 Solid Film
 Solid run in Solution
 Mull Technique
 Pressed Pellet Technique
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10. › For Liquids
 Sample is Sandwitched Between Alkyl Halides
› For Gases
 The path length is 10 cms and plain tubular endings are supplied
as standard
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11.  Detectors:
 Golay cell
 Pyroelectric Detector
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Change in detector temp. by
IR absorption changes lattice
spacing and polarization –
charge moves.
Fast response time: 1µs-1ms
Ignore steady background

12.  Photon Detector
 Semiconductor Detector
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13. 13

14.  Fourier Transform Infrared (FT-IR) spectrometry was developed in
order to overcome the limitations encountered with dispersive
instruments.
› Ability to measure all wavelength simultaneously rather then
individually.
 The interferometer produces a unique type of signal which has all
of the infrared frequencies “encoded” into it.
 Beamsplitter
 Interferogram
 Fourier transformation.
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16.  Some of the major advantages of FT-IR over the
dispersive technique include:
› Speed
› Sensitivity
› Mechanical Simplicity
› Internally Calibrated: These instruments employ a HeNe
laser as an internal wavelength calibration standard
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17. Typical Infrared AbsorptionTypical Infrared Absorption
RegionsRegions
4000 2500 2000 1800 1650 1550 650
FREQUENCY (cm-1
)
WAVELENGTH (µm)
O-H C-H
N-H
C=O C=N
Very
few
bands
C=C
C-Cl
C-O
C-N
C-CX=C=Y
(C,O,N,S)
C N
C C
N=O N=O*

18. •C-H aldehyde, two peaks (both weak)
~ 2850 and 2750 cm-1
3000 divides
UNSATURATED
SATURATED
•C-H sp stretch ~ 3300 cm-1
•C-H sp2
stretch > 3000 cm-1
•C-H sp3
stretch < 3000 cm-1
The C-H stretching region
BASE VALUE = 3000 cm-1
THE C-H BENDING REGIONTHE C-H BENDING REGION
CH2 bending ~ 1465 cm-1
CH3 bending (asym) appears near
the CH2 value ~ 1460 cm-1
CH3 bending (sym) ~ 1375 cm-1

19. CH3CH2
1465 1460 1375
asym sym
METHYLENE AND METHYL BENDING VIBRATIONSMETHYLENE AND METHYL BENDING VIBRATIONS
these two peaks
frequently overlap
and are not resolved
C-H Bending, look near
1465 and 1375 cm-1
C
H
H
H

20. CH3CH2
1465 1460 1375
asym sym
13701380
13701390
C
CH3
CH3
C CH3
CH3
CH3
C CH3
METHYLENE AND METHYL BENDING VIBRATIONSMETHYLENE AND METHYL BENDING VIBRATIONS
geminal dimethyl
t-butyl
(isopropyl)
two peaks
two peaks
The sym methyl peak
splits when you have
more than one CH3
attached to a carbon.
ADDITIONAL DETAILS FOR SYM CH3
one peak

21.  O-H 3600 cm-1
(alcohol, free)
 O-H 3300 cm-1
(alcohols & acids,
H-bonding)
3600 3300
H-BONDED
FREE
broadens
shifts
N-H 3300 - 3400 cm-1
 Primary amines give two peaks
 Secondary amines give one peak
 Tertiary amines give no peak
N
H
H
N
H
Hsymmetric
asymmetric

22.  C N 2250 cm-1
 C C 2150 cm-1
=
==
=
The cyano group often gives a strong, sharp peak due to its
large dipole moment.
The carbon-carbon triple bond gives a sharp peak, but it is
often weak due to a lack of a dipole. This is especially true
if it is at the center of a symmetric molecule.
R C C R

23. 1810 and 1760
acid
chloride ester aldehyde
carboxylic
acid amideketone
CR
O
H
CR
O
O C R
O
CR
O
Cl
CR
O
OR'
CR
O
R
CR
O
NH2
CR
O
OH
( two peaks )
HOW THE FACTORS AFFECT C=OHOW THE FACTORS AFFECT C=O
STRETCHING VIBRATIONS
B A C
D
A
B D
CE-donating
E-withdrawing
Resonance
H-bonding
1800 1735 1725 1715 1710 1690
BASE
VALUE
anhydride

24.  Conjugation of a carbonyl with a C=C bond shifts values to
lower frequencies
 For aldehydes, ketones and esters, subtract about 25-30 cm-1
for
conjugation with C=O
 Conjugated ketone = 1690 to 1680 cm-1
 Conjugated ester = 1710 to 1700 cm-1
• The C-O band appears in the range of 1300 to 1000 cm-1
•Look for one or more strong bands appearing in this range!

25.  N=O stretching -- 1550 and 1350 cm-1
asymmetric and symmetric
stretching.
 Often the 1550 cm-1
peak is stronger than the other one.
The C-X stretching region
• C-Cl 785 to 540 cm-1
,
often hard to find amongst the
fingerprint bands!!
• C-Br and C-I
appear outside the useful range of infrared spectroscopy.
• C-F bonds can be found easily, but are not that common.

26. C=O present ?
2 C=O Peaks
OH present ?
NH present ?
C-O present ?
CHO present ?
anhydride
acid
amide
ester
aldehyde
ketone
YES
YES
NO

27. C=O present ?
OH present ?
NH present ?
C-O present ?
C=N present ?
C=C present ?
C=C present ?
alcohol
amine
ether
nitrile
alkyne
alkene
aromatic
NO2 present ? nitro cpds
C-X present ? halides
(benzene ?)
NO
YES
=
=

28. C=O present ?
2 C=O Peaks OH present ?
OH present ?
NH present ?
NH present ?
C-O present ?
C-O present ?
CHO present ?
C=N present ?
C=C present ?
C=C present ?
anhydride
acid
amide
ester
aldehyde
ketone
alcohol
amine
ether
nitrile
alkyne
alkene
aromatic
NO2 present ? nitro cpds
C-X present ? halides
(benzene ?)
YES
YES
NO
YES
NO
=
=

29. acid
THE MINIMUM YOU NEED TO KNOW
OH 3600
NH 3400
CH 3000
C N 2250
C C 2150
C=O 1715
C=C 1650
C-O 1100
3300 3100 2900 2850
2750
3000
1800 1735 1725 1715 1710 1690
=C-H -C-H
-CHO
C-H
ketone
esteracid
chloride
aldehyde amide
anhydride : 1810 and 1760
CH2 and CH3 bend : 1465 and 1365
BASE VALUES
benzene C=C : between 1400 and 1600
EXPANDED CH
EXPANDED C=O

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31. 31

32. 1. Determination of Functional Group of the unknown Substance
2. Identification of Substance
3. Determination of Molecular Weight
4. Studying the Progress of Reaction
5. Detection of Impurities
6. Determination of Purity
7. Forensic investigations
8. Polymer analysis
9. Foods research
10. Quality assurance and control
11. Environmental and water quality analysis methods
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Application of IR Spectroscopy

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Refernces
1. Stuart Barbara; “Infrared Spectroscopy: Fundamentals and
Principles”; Wiley Publications.
2. William Kemp; “Organic Spectroscopy”; 3rd
edition; 1991;
McMillan Publishers.
3. Cross A.D. and Jones R. Alan; “An Introduction to Practical
Infrared Spectroscopy”; 3rd
edition; Butterworth and Co.
Publishers Ltd.
4. Galen W. Ewing; “Instrumental methods of chemical analysis”;
5th
edition; 1985; McGraw Hill Book Company.

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‘Success is the ability to go
from failure to failure
without losing our
enthusiasm’
Thank
you