Introduction of Spectroscopy Spectroscopy is the study of the interaction between matter and radiated energy or radiation. IR spectroscopy: Infrared spectroscopy (IR spectroscopy) is the spectroscopy that deals with the infrared region of the electromagnetic spectrum, that is light with a longer wavelength and lower frequency than visible light. Principle of IR spectroscopy  Molecules are made up of atoms linked by chemical bonds. The movement of atoms and the chemical bonds like spring and balls (vibration)  IR radiation does not have enough energy to induce electronic transitions as seen with UV Types of IR region  Infrared region  LIMIT OF RED LIGHT: 800 nm, 0.8 m, 12500 cm-1  NEAR INFRARED: 0.8 -2.5 m, 12500 - 4000 cm-1  MID INFRARED: 2.5 - 25 m, 4000 - 400 cm-1  FAR INFRARED: 25 - 1000 m, 400 - 10 cm-1 Molecular vibrations There are 2 types of vibrations: 1. Stretching vibrations 2. Bending vibrations  Stretching vibrations Vibration or oscillation along the line of bond  Change in bond length  Occurs at higher energy: 4000-1250 cm-1  2 types: a) Symmetrical stretching b) Asymmetrical stretching Symmetrical stretching: 2 bonds increase or decrease in length simultaneously Bending vibrations  Vibration or oscillation not along the line of bond  These are also called as deformations  Occurs at low energy: 1400-666 cm-1  2 types: a) In plane bending: scissoring, rocking b) Out plane bending: wagging, twisting

1. Presentation of
IR Spectroscopy

2. Welcome
To
My Presentation

3. Name: Md. Zahirul Islam
Roll:333
Batch:12th
Department of pharmacy
World University of Bangladesh

4. Introduction of Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated
energy or radiation

5. IR spectroscopy
Infrared spectroscopy (IR spectroscopy) is the spectroscopy
that deals with the infrared region of the electromagnetic
spectrum, that is light with a longer wavelength and
lower frequency than visible light .

6. Principle of IR spectroscopy
 Molecules are made up of atoms linked by chemical bonds.
The movement of atoms and the chemical bonds like spring
and balls (vibration)
 IR radiation does not have enough energy to induce
electronic transitions as seen with UV

7. Types of IR region
 They are divided into 3 regions
 Near IR Region
 Middle IR Region
 Far IR Region
IR region: 0.8 µm
(800nm) to 1000
µm (1mm)
Near IR: 0.8-2
µm
Middle IR: 2-15
µm
Far IR: 15-1000
µm

8. Characteristic Vibrational Frequencies of Bonds
Bonds are not rigid but behave like a spring with a mass at either end.
Obey Hooke’s Law: F = -kx - sign is motion in negative site
This gives rise to a characteristic frequency for the vibration:
m1 and m2 = Mass of the Atoms in grams in particular bond
k = Force constant of the bond.
C= velocity of the radiation = 2.998 x cm sec-1
massreduced
k
_2
1

 
21
21
_
mm
mm
massreduced



9. Molecular vibrations
There are 2 types of vibrations:
1. Stretching vibrations
2. Bending vibrations

10. Stretching vibrations
 Vibration or oscillation along the line of bond
 Change in bond length
 Occurs at higher energy: 4000-1250 cm-1
 2 types:
a) Symmetrical stretching
b) Asymmetrical stretching

11. Symmetrical stretching:
2 bonds increase or decrease in length
simultaneously.
H
H
C

12. Asymmetrical stretching
in this, one bond length is increased and
other is decreased.
H
H
C

13. Bending vibrations
 Vibration or oscillation not along the line of bond
 These are also called as deformations
 Occurs at low energy: 1400-666 cm-1
 2 types:
a) In plane bending: scissoring, rocking
b) Out plane bending: wagging, twisting

14. Scissoring
 This is an in plane blending
 2 atoms approach each other
 Bond angles are decrease H
H
CC

15. Rocking
Movement of atoms take place in the same direction.
H
H
CC

16. Wagging
2 atoms move to one side of the plane. They move up and
down the plane.
H
H
CC

17. Twisting
One atom moves above the plane and another atom moves below the
plane.
H
H
CC

18. Application of IR spectroscopy
1. Identification of Substances
2. The “Fingerprint” Region (1200 to 700 cm-1) :
3. Computer Search Systems:
4. . Determination of Molecular Structure
5. Studying Progress of Reactions
6. Detection of Impurities
7. Isomerism in Organic Chemistry
8. Presence of Water in Sample
9. Measurement of Paints & Varnishes

19. Advantage of IR spectroscopy
1. Detection (health condition)
2. Prevention (early diagnosis)
3. Monitoring
4. Diagnosis (under investigation)
5. Application of IR spectroscopy as a analytical tool varies widely
from one laboratory to other.
6. Quantitative IR analysis is based on Beer’s law.

20. Limitation of IR spectroscopy
 With IR spectroscopy it is not possible to know molecular weight of
substance.
 It is frequently non-adherence to Beer’s law of complexity spectra.
 The narrowness of spectra and effect of stray radiations make the
measurements of absorbance upon slit width and wavelength setting.
 Generally, IR spectroscopy does not provide information of the
relative positions of different functional groups on a molecule.

21. Thanks
To
all