INFRA-RED SPECTROSCOPY

Siddharth Kumar SahuM.Pharmacy

IR spectroscopy is deals with the interaction of infrared region of the electromagnetic spectrum with the matter.

It concerned with the study of absorption of infrared radiation, which causes vibrational transition in the molecule.

It is based on absorption spectroscopy.

IR-radiation

vibration changes

in electrons

IR spectrum

Introduction

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Middle IR:2.5-25 mm

IR region:0.8-1000 mm

(800nm-1mm)

Far IR:25-1000

mm

Near IR:0.8-2.5 mm

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Molecular Vibration(The dipole moment of the molecule must change as a result

of a molecular vibration.)MOLECULA

R VIBRATION

S

Fundamental Vibrations

Stretching

Vibration

Symmetric

Asymmetric

Bendin

g Vibratio

nIn-planeBending

Scissoring

Rocking

Out Of Plane

Bending

Wagging

Twisting

Non-fundamental Vibrations

Over Tones,

Combination

Tones,Fermi

Resonance

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Types of Fundamental Vibration

1. Change in the bond length b/w 2 atoms.

2. It requires more energy so appear at shorter wavelength.

Types:-1. Symmetrical stretching2. Asymmetrical stretching

STRETCHING VIB.

1. Change in the bond angle b/w two bonds.

2. It requires less energy so appear at longer wavelength.

Types:-1. In plane bending2. Out plane bending

BENDING VIB.

Stretching Mode

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Stretching Vibration • B.) Asymmetrical

stretching:

• in this, one bond length is increased and other is decreased.

• A.) Symmetrical stretching:

• 2 bonds increase or decrease in length simultaneously.

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Bending Vibration a) In plane bending- all the atom are same plane.b) Out plane bending- 2 atom, 1 same plane & 1 atom is on opposite plane.

b.) Out plane bendingi. Wagging:• 2 atoms move to one

side(up & down) of the plane.

ii. Twisting:• 2 atom where 1moves

above & 1 moves below the plane.

a.) In plane bendingi. Scissoring:• Bond angles are

decrease.

ii. Rocking:• Movement of atoms is

same direction.

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NON-FUNDAMENTAL

OVER TONES:These are

observed at twice the

frequency of strong band.Ex: carbonyl

group.

COMBINATION TONES:

Weak bands that appear

occasionally at frequencies that

are sum/difference

of 2 or more fundamental

bands.

FERMI RESONANCE:

Interaction b/w fundamental vibration & overtones or combination

tones.Ex: CO2

NON-FUNDAMENTAL VIBRATIONS

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Structure Determination of Organic Compounds through Infrared

Spectroscopy• Parameters• The spectrophotometer give the spectra of certain

wave by indicating the quality of wave and the quantity of wave that how much wave is absorbed by the molecule (Transmittance).

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The IR Spectrum• There are two type of IR Spectra from which we can

obtained the information about the quality of molecule . • The Functional Group region: Identifies the functional group

with the consequence of changing stretching vibrations. Ranges from 4000 to 1600 cm-1.

• The Fingerprint region: Identifies the exact molecule with the consequence of changing bending vibrations. Ranges from 1600 to 625cm-1.

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Instrumentation

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TYPES OF IR INSTRUMENTS

• Filters used for wavelength selection & having sample specific Detector

1. Non- Dispersive

• Sequential scanning of each wave number takes place 2.Dispersive

• Widely applied and quite popular in the far-IR and mid-IR spectrometry.

3. FTIR systems

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SOURCE1. Nernst glower Heated rare earth

oxide rod (zirconium, yttria, thoria) (temp. 1500*C)

7100 cm-1 rad. (mid to far IR)

2. Globar Heated silicon carbide rod (1500*C)

5200 cm-1rad. (mid to far IR)

3. W filament lamp 1100*C (near IR )

4. Hg arc lamp Hg plasma (far IR)

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3. Tungsten Filament Lamp

4. Hg & Xe Arc Lamp

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MONOCHROMATORSMonochromators Composed Types1. Prismatic glass/quartz &

coated by alkyl halide ( NaCl )

I. Mono pass P.M.II. Double pas

P.M.

2. Grating Grooves or lines made up of Al.

I. Reflection Grating II. Transmittance

Gratings

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DetectorsName Composed Advantage S.N

1.

2.

3.

4.

5.

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1. Thermocouple detector

2. Bolometer - Wheatstone bridge

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Dispersive IRo Double-beam instruments are mostly used than Single beam

instrument.o In dispersive IR sequential scanning of wave numbers of light

takes place.Instrumentation• In double beam spectrometer, beam separates into two and

passes to sample & reference. • Prismatic monochromators have been replaced with Grating

monochromator.

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Fourier Transform IR Instrument

o FTIR collects all wavelengths simultaneously and scans at once.

o FTIR works based on Michelson Interferometer which having

• Beam splitter• Fixed mirror• Movable mirror

21Interferometer

He-Ne gas laser

Fixed mirror

Movable mirror

Sample chamber

Light source

Detector

Beam splitter

FTIR Instrumentation

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General Purpose Of IR Radiation

Infrared light is used in industrial, scientific, and medical applications.

• In Telescopes to detect  planets• Finding heat leaks from houses• Infrared thermal-imaging cameras are used to detect heat loss

in insulated systems,• to observe changing blood flow in the skin,• to detect overheating of electrical apparatus.• Night-vision devices• Remote temperature sensing, short-ranged 

wireless communication, spectroscopy, and weather forecasting.

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Pharmaceutical Applications

Qualitative determination of substances

Structural elucidation by determining the functional groups.

Detection of impurities

Identification of geometrical isomers for both organic & inorganic samples

Detection of presence of water in sample

Quantitative determination of sample by using Beer’s-Lamberts law

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REFERENCE• Chatwal G.R. . A textbook of ‘Instrumental Method

Of Chemical Analysis’. • www.Slideshare.com • instrupres-140329002030-phpapp01• uttam-ir-140929003810-phpapp02• irspectroscopy-140210002609-phpapp01

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TYPES OF VIBRATIONS

Stretching Mode

In plane bending vibrations

Scissoring

Rocking

Out plane bending vibrations

Wagging

Twisting

Symmetric

Asymmetric