Introduction and Principle of IR spectroscopy
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Transcript of Introduction and Principle of IR spectroscopy
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Introduction and Principle of IR Spectrophotometry
Presented by:Rajaram KshetriB.pharm, IOM
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Contents
• Introduction of Spectroscopy
• Introduction of IR spectrophotometry
• Principle of IR spectrophotometry
• Molecular vibrations
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Spectroscopy
• Method of “Seeing the unseeable”
• using electromagnetic radiation to obtain information about atoms and molecules that are too small to see.
AtomsMolecules
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Spectroscopy is an instrumentally aided study of the interactions between matter (sample being analyzed) and energy (any portion of the electromagnetic spectrum)
EMR ANALYTE SPECTROPHOTOGRAPH
1.UV-Visible radiations--------excitation of electrons---------UV-visible spectrum
2.IR-radiations------------------vibration changes in electrons--------IR spectrum
3.Radio frequency---------------spin rotational changes-------------N.M.R spectrum
Conc. should be lower
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IR spectrophotometry
Energy of molecule = Electronic energy+ Vibrational energy + Rotational energy
• IR spectroscopy is concerned with the study of absorption of infrared radiation, which causes vibrational transition in the molecule.
Hence, IR spectroscopy also known as Vibrational spectroscopy.
• IR spectra mainly used in structure elucidation to determine the functional groups.
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• IR region: 0.8 µm (800nm) to 1000 µm (1mm)
1.Near IR: 0.8-2 µm2.Middle IR: 2-15 µm3.Far IR: 15-1000 µm
Most of the analytical applications are confined to the middle IR region because absorption of organic molecules are high in this region.
Sub divided into
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Principle of IR spectroscopy• Molecules are made up of atoms linked by chemical
bonds. The movement of atoms and the chemical bonds like like spring and balls (vibration)
• This characteristic vibration are called Natural frequency of vibration.
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• When energy in the form of infrared radiation is applied then it causes the vibration between the atoms of the molecules and when,
Applied infrared frequency = Natural frequency of vibration
Then, Absorption of IR radiation takes place and a peak is observed.
Different functional groups absorb characteristic frequencies of IR radiation. Hence gives the characteristic peak value.
Therefore, IR spectrum of a chemical substance is a finger print of a molecule for its identification.
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Criteria for a compound to absorb IR radiation
1. Correct wavelength of radiation 2. Change in dipole moment
1. Correct wavelength of radiation: A molecule to absorb IR radiation, the natural
frequency of vibrations of some part of a molecule is the same as the frequency of incident radiation.
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2. Change in dipole moment
• A molecule can only absorb IR radiation when its absorption cause a change in its electric dipole
• A molecule is said to have an electric dipole when there is a slight positive and a slight negative charge on its component of atoms.
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Molecular vibrationsThere are 2 types of vibrations:1.Stretching vibrations2.Bending vibrations
1. 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 stretchingb) Asymmetrical stretching
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a) Symmetrical stretching:
2 bonds increase or decrease in length simultaneously.
H
H
C
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b) Asymmetrical stretching
• in this, one bond length is increased and other is decreased.
H
H
C
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2. Bending vibrations
• Vibration or oscillation not along the line of bond
• These are also called as deformations• In this, bond angle is altered• Occurs at low energy: 1400-666 cm-1
• 2 types:a)In plane bending: scissoring, rockingb)Out plane bending: wagging, twisting
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a) In plane bendingi. Scissoring:• This is an in plane blending• 2 atoms approach each other• Bond angles are decrease
H
H
CC
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ii. Rocking:• Movement of atoms take place in the same
direction.
H
H
CC
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b) Out plane bending
i. Wagging:• 2 atoms move to one side of the plane. They move
up and down the plane.ii. Twisting:• One atom moves above the plane and another
atom moves below the plane.
H
H
CC
H
H
CC