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CONTENTS Introduction to spectroscopy Infrared spectroscopy Theory and principle Advanced infrared spectroscopy techniques Applications Conclusion 2


WHAT IS S PECTROSCOPY ..?? DEFINITION : Spectroscopy is the measurement and interpretation of electromagnetic radiation (EMR)which is absorbed (or) emitted (or) polarized (or) dispersed (or) scattered (or) refracted (or) reflected (or) transmitted when the molecules or atoms or ions of a sample move from one energy state to another state. 3

Common types of spectroscopy ::

C ommon t ypes o f s pectroscopy : Atomic spectroscopy Molecular spectroscopy Visible Ultraviolet Infrared Raman Nuclear magnetic resonance Electron spin Mass 4


INFRARED SPECTROSCOPY IR spectroscopy : Infrared spectroscopy is the subset of spectroscopy that deals with the infrared region of the electromagnetic spectrum. It covers a range of techniques, the most common being a form of absorption spectroscopy. Wavelength The wavelength range of infrared radiation lies between 14000–10 cm −1 (0.8–1000 μm) . The most useful I.R. region lies between 4000 - 670cm -1 . Regions Near infrared :- approximately 14000–4000 cm −1 (0.8–2.5μm) Mid infrared :- approximately 4000–400 cm −1 (2.5–30μm) Far infrared :- approximately 400–10 cm −1 (30–1000 μm) 5


THEORY AND PRINCIPLE CORRECT WAVELENGTH OF RADIATION In any molecule, atoms or groups of atoms are connected by bonds ,which will be in a continuous motion & will exihibit some frequency.This frequency is called as natural frequency. A molecule absorbs radiation only when natural frequency = incident frequency . After absorbing the correct wavelength of radiation, the molecule vibrates and absorption of infrared radiation takes place and a peak is observed. 6

When the molecule absorbs ir radiation…????:

When the molecule absorbs ir radiation…???? A molecule can absorb IR radiation when its absorption causes a change in its electric dipole. Molecule is said to have an electric dipole when there is a slight positive and negative charge. When the molecule having an electric dipole is kept in the electric field ,this field will exert forces on the electric charges in the molecules. 7

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When charged atoms vibrate, they absorb infrared radiation from radiation source. If rate of vibration at charged atoms in a molecule is fast, absorption of radiation is intense and thus IR spectrum will have intense absorption bands. If rate of vibration is slow, weak bands will appear in IR spectrum. 8

Modes of vibrations:

Modes of vibrations 1. STRETCHING : Change in inter-atomic distance along bond axis. It is of two types: Symmetrical Asymmetrical Bonds increase or decrease One bond length increases in length symmetrically. and the other decreases. 9

Modes of vibrations:

Modes of vibrations 2. BENDING : Change in angle between two bonds. There are four types of bend. Rocking Scissoring Bond angle is maintained, but Bond angle decreases. both bonds move within the plane . 10

Modes of vibrations:

Modes of vibrations Wagging 11 B oth atoms move to one side of plane . Twisting One atom is above the plane and the other is below the plane

Instrumentation :

Instrumentation 1. Sources 2. Monochromators 3. Sample preparation 4. Detectors 5. Typical method 12

1. Sources :

1. Sources An inert solid is electrically heated to a temperature in the range 1500-2200 K. The heated material will then emit infrared radiation. Nernst glower Globar source Incandescent wire source Mercury arc 13

2. Monochromators :

2. Monochromators A monochromator is an optical device that transmits a mechanically selectable narrow band of wavelengths of light or other radiation chosen from a wider range of wavelengths available at the input. Two types of monochromators are : Prism monochromator Grating monochromator 14

3. Sample preparation :

3. Sample preparation Solid samples - Solid run in solution - Solid films - Mull techniques - Pressed pellet techniques Liquid samples Gaseous samples 15

4. Detectors :

4. Detectors Thermocouples Photo conducting Bolometers Thermistors Semiconductor detector Pyroelectric detectors 16

5. Typical method :

5. Typical method 17

Ir instrument:

Ir instrument 18

Advanced infrared spectroscopy techniques:

Advanced infrared spectroscopy techniques 1. Fourier transform spectroscopy 2. Two-dimensional infrared spectroscopy 3. Nonlinear two-dimensional infrared spectroscopy 19



IR Spectrum of Decane:

IR Spectrum of Decane 21

Ir Spectrum of mineral oil:

Ir Spectrum of mineral oil 22

Ir spectrum of cyclohexane:

Ir spectrum of cyclohexane 23


alkenes 24

IR Spectrum of 1-Hexene:

IR Spectrum of 1-Hexene 25

Ir spectrum of cyclohexene:

Ir spectrum of cyclohexene 26

Ir spectrum of cis-2-pentene:

Ir spectrum of cis-2-pentene 27

Ir spectrum of trans-2-pentene:

Ir spectrum of trans-2-pentene 28

Aromatic rings:

Aromatic rings 29



Ir spectrum of ortho-diethyl benzene:

Ir spectrum of ortho-diethyl benzene 31

Ir spectrum of meta-diethylbenzene:

Ir spectrum of meta- diethylbenzene 32

Ir spectrum of para-diethylbenzene:

Ir spectrum of para-diethylbenzene 33

Ir spectrum of styrene:

Ir spectrum of styrene 34

Alcohols & phenols:

Alcohols & phenols 35

IR Spectrum of 1-Hexanol:

IR Spectrum of 1-Hexanol 36

Ir spectrum of 2-butanol:

Ir spectrum of 2-butanol 37

Ir spectrum of para-cresol:

Ir spectrum of para-cresol 38

Alcohols & phenols:

Alcohols & phenols 39


aldehydes 40

IR Spectrum of benzaldehyde:

IR Spectrum of benzaldehyde 41

Ir spectrum of nonanal:

Ir spectrum of nonanal 42

Ir spectrum of crotonaldehyde:

Ir spectrum of crotonaldehyde 43


ketones 44

IR Spectrum of Mesityl oxide:

IR Spectrum of Mesityl oxide 45

Ir spectrum of acetophenone:

Ir spectrum of acetophenone 46

Ir spectrum of cyclopentanone:

Ir spectrum of cyclopentanone 47

Carboxylic acids:

Carboxylic acids 48

IR spectrum of Isobutyric acid:

IR spectrum of Isobutyric acid 49

Ir spectrum of benzoic acid:

Ir spectrum of benzoic acid 50


amines 51

IR Spectrum of Butylamine:

IR Spectrum of Butylamine 52

Ir spectrum of dibutylamine:

Ir spectrum of dibutylamine 53

Ir spectrum of tributylamine:

Ir spectrum of tributylamine 54

Heteroaromatic compounds:

Heteroaromatic compounds Hetero aromatic compounds such as Furan,Thiophene etc show C-H stertching bands in the region of 3077-3000 cm -1. Compounds containing N-H group shows,N-H Stretching absorption in the region 3500-3220cm -1 . In this region of absorption,the exact position depends upon the degree of hydrogen bonding and hence upon the physical state of the sample or the polarity of the solvent. 55

Hetero aromatic compounds:

Hetero aromatic compounds Pyrrole and Indole in dilute solution in non-polar solvents show a sharp band near 3495cm -1 . Ring stretching vibration occur in general region between 1600-1300cm -1 . The absorption involves stertching and contraction of all the bonds in the ring and interaction between these stretching modes. 56

applications in organic compounds:

applications in organic compounds Determination of molecular structure: From an examination of positions of absorption bands in the spectrum, it is easy to establish the nature of groups present in molecule. Studying the progress of reactions Detection of impurities Isomerism in organic chemistry 57

Applications of Infrared Spectroscopy to Quantitative Analysis:

Applications of Infrared Spectroscopy to Quantitative Analysis Used to determine the concentration of one of the functional groups of the compound to be estimated. E.g.: Mixture of Hexane and Hexanol. Concentration can be known by using Beer-lamberts law. Two methods are used to determine absorptivity They are : 1.Cell-in cell-out method 2.Baseline method 58

Miscellaneous examples::

Miscellaneous examples: A) Determination of purity : If impurity is present in a compound it reduces sharpness of individual bands causes appearance of extra bands and a general blurring of spectra. B) Shape of symmetry of a molecule C) Measurement of paints and varnishes D) Examination of old paintings E) In industry : To determine the impurities of raw material 59

Recent applications of IR spectroscopy :

Recent applications of IR spectroscopy 1. Imaging of human hair 2. Atmosphere and the Environment 3. Combustion and Fire Detection 4. Measuring Electric and Magnetic Fields 5. Spectroscopy and Technique Development 6. Process Monitoring and Industrial Hygiene 7. Forensic Applications 60


Conclusion Infrared spectroscopy is a most important analytical technique. Despite of of short comings it has proved to be one of the most valuable methods for characterizing, both qualitatively and quantitatively the multitude of organic compounds and mixtures of compounds encountered in research and industry. 61


REFERENCES Donald L.Pavia, Gary M.Lampman, George S.Kriz; Introducion to spectroscopy; Third edition; pg:1-72. Dr.B.K.Sharma; Instrumental methods of chemical analysis; Eighteenth Edition 1999; pg:71-83. Robert M.Silverstein, Francisx.Webster; spectrometric identification of organic compounds; Sixth edition 1996; pg:87-88. Gurdeep.R.Chatwal, Sham. K.Anand; Instrumental methods of chemical analysis; First edition 1979; pg:2.62-2.75. 62


REFERENCES William Kemp; organic spectroscopy; Third edition; pg: 55-56. Y.R.Sharma; Elementary organic spectroscopy (principles& chemical applications); Fourth edition; page:133,137-140. www.google.wikipedia.org 63

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