1. Infrared spectroscopy can be used to qualitatively and quantitatively analyze compounds. It is used to identify unknown substances by comparing their IR spectra to reference standards. 2. The "fingerprint" region from 1200-700 cm-1 is particularly useful for identification because small molecular differences result in significant spectral changes in this region. Computer search systems can also identify compounds by matching IR spectra to profiles of pure compounds. 3. IR spectroscopy allows determination of molecular structures by identifying the presence or absence of functional groups from their characteristic absorption bands. It can also be used to study the progress of chemical reactions.

1. APPLICATIONS OF IR
SPECTROSCOPY
Presented by:
Muhammed Fahad
1st M.Pharm

2. QUALITATIVE ANALYSIS
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3. 1. Identification of Substances
• To compare spectrums.
• No two samples will have identical IR
spectrum.
• Criteria: Sample and reference must be tested
in identical conditions, like physical state,
temperature, solvent, etc.
• Disadvt: Enantiomers cannot be distinguished
(spectrum are identical).
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4. The “Fingerprint” Region (1200 to 700 cm-1):
• Small differences in structure & constitution of
molecule  result in significant changes in the
peaks in this region.
• Hence this region helps to identify an
unknown compound.

6. Computer Search Systems:
• Newer IR instruments offer computer search
systems to identify compounds from stored
infrared spectral data.
• The position and magnitudes of peaks in the
spectrum is compared with profiles of pure
compounds stored.
• Computer then matches profiles similar to that of
the analyte and result is displayed.

8. 2. Determination of Molecular
Structure
• Used along with other spectroscopic
techniques.
• Identification is done based on position of
absorption bands in the spectrum.
• Eg.: C=O at 1717 cm-1.
• Absence of band of a particular group
indicates absence of that group in the compd.
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9. 3. Studying Progress of Reactions
• Observing rate of disappearance of
characteristic absorption band in reactants; or
• Rate of increasing absorption bands in
products of a particular product.
• Eg.: O—H = 3600-3650 cm-1
C=O = 1680-1760 cm-1
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10. 4. Detection of Impurities
• Determined by comparing sample spectrum
with the spectrum of pure reference
compound.
• Eg.: ketone impurity in alcohols.
• Detection is favoured when impurity possess a
strong band in IR region where the main
substance do not possess a band.
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11. 5. Isomerism in Organic Chemistry
(i) Geometrical Isomerism:
• trans isomers give a simpler spectrum than
cis due to symmetry.
(ii) Conformers (Rotational Isomers):
• Identified with the help of high resolution IR
spectrometers.
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12. Contd…
• E.g.: Ethanol
normal OH – 3636 cm-1
weak band – 3622 cm-1
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13. (iii) Tautomerism:
Existence of 2 or more chemical compds capable
of intercovertion , usually by exchanging a
hydrogen atom between the 2 atoms.
e.g.: Thiocarboxylic acid
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14. 6. Functional Group Isomerism
• Isomerism shown by compounds having same
molecular formula but different functional
groups.
Eg: CH3–O–CH3 and CH3–CH2–OH
(Diethyl ether) (Ethanol)
OH = 3500-3100 cm-1
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15. 7. APPLICATIONS OF IR SPECTROSCOPY TO
INORGANIC COMPLEXES
Difficulties:
1. High modes of vibration:
Since they contain more than 5 atoms; hence min. 10
modes of vibrations.
2. Lower symmetry of Complexes:
Due to formation of ligand & polynuclear complexes.
3. Formation of chelates:
Large no. of new bands appear.
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16. APPLICATIONS OF IR SPECTROSCOPY TO
INORGANIC COMPLEXES
Assumptions (not always true):
1. Complex formation only affects the vibrations of
the ligand slightly.
2. Vibrations do not undergo coupling with other
vibrations of another ligand.
3. When ligand is coordinated with another atom,
it will not change the symmetry of the ligand.
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17. Geometrical Isomerism:
Eg: Bipyridyl cobalt (III) chloride
[Co(Bipy)2(Cl2)Cl]
2 isomers – trans isomer has more symmetry
than cis isomer. Hence complex spectrum is
expected for cis isomer.
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APPLICATIONS OF IR SPECTROSCOPY TO
INORGANIC COMPLEXES

18. 8. Shape of Symmetry of a Molecule
• E.g.: Nitrogen dioxide, NO2
If linear --> only 2 bands should be present.
If bent --> 3 bands should be present.
Actual spectrum shows 3 peaks at 750, 1323 and
1616 cm-1.
• Similarly, IR spectrum was used to determine
structures of XeF2, XeF4 & XeF6  linear, square
planar and octahedral resp.:
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19. 9. Identification of Functional Groups
Due to the presence of functional group region.
E.g.:
(3500-3100 cm-1) (1700 cm-1)
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20. 10. Presence of Water in Sample
• If lattice water is present, spectra will contain 3
characteristic bands  at 3600-3200 cm-1, 1650
cm-1 and 600-300 cm-1.
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21. 11. Measurement of Paints &
Varnishes
• Measured by ‘reflectance analysis’
• Advt: Measure IR absorbance of paints on
appliances or automobiles without destroying the
surface.
• Make and year of car can be determined from IR
spectral analysis.
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22. 12. Examination of Old Paintings &
Artifacts
• Help to determine fake “masterpieces”.
• Varnish & paints from old items (statues, canvas,
etc.) are analysed by IR spectroscopy.
• Presence of new paint traces implies the
“masterpiece” is fake.
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23. 13. In Industry
1. Determine impurities in raw materials (to ensure
quality products).
2. For Quality Control checks; to determine the %
of required product.
3. Identification of materials made in industrial
research labs,
or materials of competitors.
E.g.: Impurity in bees wax (with petroleum wax)
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24. 14. Analysis of Petroleum HCs, Oil &
Grease contents
• These contain C–H bonds.
Absorption at 3100-2700 cm-1.
• ‘Freons’—Fluorocarbon-113; do not contain C–H
bond.
• Thus, quantity of HCs, oil & grease in freons is
determined by measuring C–H absorption at
2930 cm-1.
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25. 15. Quantitative Analysis of
Multicomponent Mixtures of Sulfur-oxygen
Anions by ATR Spectroscopy
• FTIR-ATR help to determine sulfur-oxygen anions in
aqueous solutions.
S–O stretching band at 1350-750 cm-1.
• ATR uses water resistant cells,
have short & reproducible effective path length.
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26. 16. Characterization of Heterogenous
Catalysts by Diffuse Reflectance
Spectroscopy
• Diffuse Reflectance Spectroscopy help to determine
nature of molecules attached to catalyst surfaces.
E.g.: characterization of olefin polymerization
catalysis with silica gel; diff. types of Si–OH bonds are
determined.
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27. 17. Analysis of Multilayered Polymeric
Film using FTIR Spectroscopy
• Determine identities of polymer materials in
multilayered film.
• FTIR helps in quick characterization.
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28. Other Applications
1. Determination of unknown contaminants in
industry using FTIR.
2. Determination of cell walls of mutant & wild
type plant varieties using FTIR.
3. Biomedical studies of human hair to identify
disease states (recent approach).
4. Identify odour & taste components of food.
5. Determine atmospheric pollutants from
atmosphere itself.
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29. QUANTITATIVE ANALYSIS
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30. QUANTITATIVE ANALYSIS
• Based on the determination of one of the
functional groups.
E.g.: concn of hexanol in hexane-hexanol mixture.
A = -log I1/I0 = abc (Beer-Lambert’s law)
A = Absorbance
I0 = Intensity of radiation before entering the sample
I1 = Intensity of radiation after leaving the sample
a = Absorptivity of the solution
b = Initial path length of the sample cell
c = concn. of the solution
If ‘b’ & ‘a’ are const., then ‘A’ α ‘c’
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31. 2 methods to determine ‘A’ and conc. ‘c’:
1. Cell-in cell-out Method:
Std. calibration curve method
2. Baseline Method:
 selection of suitable absorption band
 P0 & P are measured
 Abs, log (P0/P) plotted against conc; determine
unknown
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32. Baseline Method:
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33. Advantages:
1. Common possible errors are eliminated.
2. Same cell is used for all determinations.
3. All measurements are done on points defined by
the spectrum; hence no dependence on λ
intensity.
4. Eliminate changes in instrument sensitivity and
source intensity.
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34. Using KBr Pellets (Disk Technique):
 Uniform pellets of similar weight & thickness
 Known wts. of KBR + known qty of test
 Calibration curve plotted
 Disks are weighed and thickness measured
Using Internal Std. (pot. thiocyanate):
 Dried, ground with KBr to make a conc of 0.2% by wt
of thiocyanate.
 Calibration curve plotted.
 Ratio of thiocyanate absorption at 2125 cm-1 to a
chosen band of test is plotted vs conc.
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