This document discusses the application of infrared spectroscopy in research. It begins by introducing the electromagnetic spectrum and infrared region. It then covers the principles of IR spectroscopy, including how molecular vibrations can be observed in IR spectra. Factors that determine peak positions, intensities, and widths are explained. Common vibrational modes like stretching and bending are described. The document discusses interpreting IR spectra for organic compounds, including distinguishing functional groups and molecular structure. It also covers practical aspects, applications in various fields like pharmaceutical research and quality control, and limitations of IR analysis.

1. 1
APPLICATION OF INFRA RED
SPECTOSCOPY IN RESEARCH
Vijay Kumar Bansal
Associate prof.
Dept. of Pharmaceutical Chemistry
LACHOO MEMORIAL COLLEGE OF SCIENCE AND TECHNOLOGY, PHARMACY
WING, JODHPUR

2. OBJECTIVES
 Introduction of electromagnetic spectrum and
Infra red spectrum
 The principles of infrared spectroscopy
 Factors that determine the positions and
intensities of bands in infrared spectra.
 Interpretation of infrared spectra.
 Practical aspect of IR spectroscopy
 Major areas of applications

3. Electromagnetic Waves
Molecules absorbs IR radiations and vibrate

4. The principles of infrared spectroscopy
What is spectroscopy:
 Infrared energy is absorbed as vibrations of polar
molecules when sample is placed in IR beam
 Only vibrations that cause a change in dipole
moment give rise to bands in IR spectra
 The patterns of absorption (wavelengths absorbed
and to what extent) are called ‘spectra’.
 The field of spectroscopy is concerned with the
interpretation of spectra in terms of atomic and
molecular structure (and environment).

5. Regions of spectrum
1. CGF region : 4000-1000 cm-1
(Characteristic Group Frequency)
2. Fingerprint region: ~1000-400 cm-1

6. Vibrations
Stretching
frequency
Bending
frequency
•Stretching frequencies are higher than bending frequencies
(it is easier to bend a bond than stretching or compresing them)
•Bond involving Hydrogen are higher in freq. than with heavier atoms
•Triple bond have higher freq than double bond which has higher freq than single bond

7. IR is used to tell:
1. what type of bonds are present
2. some structural information like functional groups
1. POSITION 2. STRENGTH 3. WIDTH
Three things are there related to bands in a IR graph

8. IR OF H2O

9. Principal that govern the vibrational
frequencies of bonds
Hooke’s law :
n
= 1
2pc
 K
m
n : Frequency in cm-1
c : Velocity of light => 3 * 1010 cm/s
K : Force constant => dynes /cm (Bond Srength)
m : Reduced mass of atoms in grams
m =
m1 m2
m1 + m2
m1 = mass of the atom 1
m2 = mass of the atom 2

10. Band Property
POSITION REDUCED MASS
BOND STRENGTH
(STIFFNESS)
LIGHT ATOMS
HIGH FREQUENCY
STRONG BONDS
HIGH FREQUENCY
STRENGTH
(INTENSITY)
CHANGE IN
‘POLARITY’
STRONGLY POLAR
BONDS GIVE
INTENSE BANDS
WIDTH HYDROGEN
BONDING
STRONG
HYDROGEN
BONDING GIVES
BROAD BANDS
Factor affecting Effect

11. Other factors that determine the
positions, intensities and shape of
bands in infrared spectra
 Coupled vibrations
 Inductive effect = +I and–I effect
 Mesomeric effect
 Field effect or Steric effect
 Hydrogen bonding

12. INTERPRETATION OF INFRARED SPECTRA.

13. Width of bands gives information
H-
bonded
OH
n(NH3
+)
C
H3
CH3
OH
COOH
Cl
Cl
Cl
H
3
C
H3
CH2
CH2
NH

14. Weak IR intensity of CC
ClCH2CCH
Intensity of bands gives information
-CC-
C-H
Strong intensity

15. 1. Most organic compounds are composed of C, H, O and N.
2. Most chemical groups have specific absorption with 4000
– 670 cm-1 . This region can be divided into 7 regions as:
No. Wavenumber Bond and vibration
1 3750 ~ 3300 νO-H, νN-H
2 3300 ~ 3000 νC-H (-C≡C-H, >C=C-H, Ar-H)
3000 ~ 2700 νC-H(CH3, CH2, CH, CHO)
3 2400 ~ 2100 νC ≡C, νC ≡N
4 1900 ~ 1650 νC=O
5 1675 ~ 1500 νC=C, νC=N
6 1475 ~ 1000 δCH, ν C-O, ν C-C
7 1000 ~ 650 γC=C-H, Ar-H, γ CH2
The 7 important region of IR spectra

16. INTERPRETATION OF AROMATIC COMPOUNDS
S.N. Frequencies cm-1 Interpretation
1. 3050-3000 =C-H Str.
2. 1600-1400 C=C Str.
Ring vibrations
3. 900-700 C-H bending
4. 2000-1600 (very weak) summation bands Due to coupling vibratoins
and overtone of C-H wagginng
Identification of ortho, para and meta substitution
4. 770-730 & 710-690 Two bands due to 5H
5. 770-735 Single band due to 4H
6. 900-860 & 810-750 Two Bands due to 1H & 3 H
7. 860-800 Single band due to 4 H
Monosubstitution
meta substitution
ortho substitution
para substitution

17. ACETOPHENONE
C
O
CH3
H
H
H
H H

18. OCH3
ANISOLE

19. Aomatic aldehyde: 4-Methoxy Benzaldehyde
C
OCH3
O
H

20. Benzamide
C
O
N
H2

21. m Cresol
OH
CH3

22. Phenyl aceteylene
C
CH

23. Spurious bands in IR spectra
Freq. (cm-1) Comment
3710 Sharp H2O peak from trace solvent.
3450-3330 Occluded H2O in sample or from KBr (also at 1640).
2920 Nujol C-H band (also 1375, 1460)
2350 Atmospheric CO2 (also at 667)
2000-1450 Atmospheric H2O vapour.
1750-1690 C=O from dissolved coating or liner.
1355 NO3 impurity in KBr (also at 823).
980 SO4 from K2SO4, maybe SO4 exchange with KBr.
795/780 CCl4 vapour/liquid from solvent.
770 CHCl3 solvent.

24. PRACTICAL ASPECT OF IR SPECTRA
1.Only 1-2 mg of sample is required with 50-
100 mg of dry KBr powder.
2. KBr and sample must be anhydrous and
dried before taking IR spectrum.
3.Compound must be pure and single entity
for interpretation of IR spectrum.
.
So Taking IR spectrum of crude plant extract
and mixture of componds is quite useless
Warning: Don’t try to over interpret your IR spectrum. Often, it is not possible to arrive at a unique structure based
on IR analysis only. One should use other physical data such as mp, bp, solubility and other spectroscopy such as NMR
and Mass.

25. APPLICATION OF IR SPECTROSCOPY
1. For structural elucidation of NCEs (new
chemical entities)
2. Screening for Counterfeit Drugs
3. Organic compounds identification
4. Identification and quantification of organic
solid, liquid or gas samples.
5. Analysis of powders, solids, gels, emulsions,
pastes, pure liquids and solutions, polymers,
pure and mixed gases.
6. Samples range in size from single fibers only
20 microns in length to atmospheric pollution
studies involving large areas.
So IR is a usefull tool For research, methods development,
quality control and quality assurance applications.

26. Pharmaceutical research
Forensic investigations
Polymer analysis
Lubricant formulation and fuel additives
Foods research
Quality assurance and control
Environmental and water quality analysis
methods
Biochemical and biomedical research
Coatings and surfactants
FIELDS OF IR APPLICATION

27. THANKS