This document discusses infrared (IR) spectroscopy, which analyzes the vibrational transitions of molecules to determine their functional groups. It describes the principle that IR radiation is absorbed when its frequency matches the natural vibration frequency of a molecule's bonds. The document outlines different types of vibrations, factors affecting frequencies, applications like pharmaceutical analysis, and provides examples of using IR spectroscopy to identify functional groups and fingerprints.

1. KARNATAKA COLLEGE OF PHARMACY
Seminar topic: IR-SPECTROSCOPY
By: KAVANA BB
1ST SEM M Pharm
Subject : MPAT
DEPARTMENT OF PHARMACEUTICAL ANALYSIS SUBMITTED TO: SRINIVAS RAO.T
ASSISTANT PROFESSOR
DEPARTMENT OF PHARMACEUTICAL ANALYSIS
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2. INTRODUCTION:
• Infrared (IR) spectroscopy, also known as vibrational spectroscopy is a
method of analysis that takes advantage of the vibrational transitions of a
molecule.
• It is used to determine the functional group.
• The IR region will be in between of uv -vis and micro wave region.
• Wavelength - 2.5 -1.5 microns ; wave no. -500-4000cm-1 .
• The technique or method of using infrared spectroscopy involves an
instrument known as an infrared-spectrometer (or a spectrophotometer) to
create the infrared spectrum.
• Condition required to use IR SEPECTROSCOPY ;
a) The molecule should have dipole movement
b) The molecule should not be symmetric.
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4. PRINCIPLE:
• The frequency of the IR radiation is equal to the natural frequency of vibration
then the molecule will observe IR radiation and peak is absorbed .When infrared
light is absorbed by a sample, it causes the bonds in the molecule to vibrate at
the same frequency as the absorbed light. The absorbed light is then absorbed
as energy by the molecule, and the molecule transitions to an excited state.
• The molecule will eventually return to its ground state, releasing the absorbed
energy as heat or light.
By measuring the absorption of infrared light at different wavelengths, it is
possible to determine the vibrational modes of the bonds in the molecule.
• Each bond in a molecule has a characteristic vibrational frequency, and the
absorption of infrared light at these frequencies can be used to identify the
molecular structure of the sample.
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5. Types of BANDS in IR SPECTRA
• Overtone bands means the molecule will excite from ground state to next energy
level i.e. V0-V1-V2.
• Combination bands means the molecule will directly excite from ground state to
second or third energy level directly i.e., V0-V2 .
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6. TYPES OF VIBRATIONS :
1. Stretching vibration: Here bond length will increases and decreases, yet the
angle of connection is still fixed.
Types of stretching vibrations
• Symmetric stretching vibration: In this case both the atoms are stretched or
compressed in the matching path.
• Asymmetric stretching vibration: In this kind of vibration only one atom
undertakes stretching while the other atom experiences compression.
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7. • Bending vibrations: Here bond length will remain same but the bond angle will
get changed .
Types of bending vibrations:
• In plane bending vibrations:
• Scissoring: Just like scissors both the atom will shift towards each other.
• Rocking: Both the atoms will shift in one similar direction, that is, either to
the left side or to the right side.
• Out of plane bending vibrations:
• Wagging: In this vibration, both the atom will move up and down keeping the
central atom permanent.
• Twisting: In this vibration, one atom moves up and another atom moves
down with a stable central atom.
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9. FINGERPRINT REGION
• The region from 1500-600 cm-1 in IR spectrum.
• In this region number of bending vibration is more than the number
of stretching vibration.
• Number of molecules contains same functional group & show similar
peak above 1500 cm-1 but they show different peak in finger print
region.
• Therefore we can say that each and every molecule have unique peak
or band which is observed in finger print region, it is just like the
finger print of human
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10. FACTORS AFFECTING VIBRATIONAL FREQUENCY
• COUPLED VIBRATION
• HYDROGEN BONDING
• ELECTRONIC EFFECTS
• FERMIC RESONANCE
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11. COUPLED VIBRATION
• IF C-H will have one stretching frequency.
• If CH2 is taken then two stretching frequency:
a) symmetric – lower wave no.
b) asymmetric –higher wave no.
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12. FERMI RESONANCE
• In overtone bands, will have the low intensity of absorption. Here the
coincide of same energy fundamental frequency and resonance will
occur that resonance is called as fermi resonance.
• Here because of affect fermi resonance wave no. will increase.
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13. Electronic effect
• Absorption frequency will change when there is change in substituent og
neighboring group .
• various electronic effect :
a) Inductive effect : + I effect – decreasing of wave no.
- I effect – increase of wave no.
a) Mesmeric effect : bond length increase, bond strength decrease leads to
decrease in force constant, results in decrease of wave no .
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14. Hydrogen bonding
• Presence of hydrogen bond in a molecule will decrease in wave no.
• Example :
1. N-H N-H : BEFORE BONDIND 3500CM-1
AFTER BONDING 3300CM-1
2. O-H O-H : 3650CM-1 (BEFORE)
3450 CM -1 (AFTER)
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15. APPLICATIONs
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16. APPLICATIONS:
• Infrared spectroscopy is widely used in both research and industry as a
simple and reliable technique for measurement, quality control and
dynamic measurement.
• Infrared spectroscopy has also been successfully utilized in the field of
semiconductor microelectronics: for example, infrared spectroscopy can
be applied to semiconductors like silicon, gallium arsenide, gallium
nitride, zinc selenide, amorphous silicon, silicon nitride, etc.
• Analysis of pharmaceutical substances.
Example; preparation of KBr or KCl disc.
• Analysis of pharmaceutical dosage form
ex; determination of aspirin ,phenacetin and caffeine in tablets .
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17. • ANALYTICAL CHEMISTRY EX; distinguish primary, secondary, and tetra
amine salts from one another.
• Identification of functional groups.
• Identification of fingerprints.
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18. THANK YOU
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