University of Petra
Faculty of Science & Arts
Department of Chemistry
Seminar
I.R Spectroscopy
By
Firas Al-ouzeh
Supervisor : Nuha I. Swidan
Summer 2007
1
Outline
- What is spectroscopy?
- Electromagnetic spectrum .
- IR active and inactive .
- Infrared spectroscopy .
- IR instrument.
- Region of infrared spectrum
- Fingerprint molecule.
- IR table. - Infrared energy mode. 2
Outline
-Vibration modes leading to IR absorption.
- How to prepare IR sample. - FT-IR spectrometer. - References -
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-
What is Spectroscopy?
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Shine light (energy) on a sample to
determine what is inside
Measure the amount of electromagnetic
radiation absorbed and/or emitted by a
compound
Different molecules absorb at different
energies
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Electromagnetic Spectrum
Each form of spectroscopy uses a different part
of the electromagnetic spectrum
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IR-Active and Inactive
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A polar bond is usually IR-active.
A nonpolar bond in a symmetrical
molecule will absorb weakly or not at all.
=>
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Infrared Spectroscopy
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Evaluates covalent bond stretching
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Infrared (IR) spectroscopy measures the bond vibration frequencies
in a molecule and is used to determine the functional group.
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IR spectra allow one to determine the presence or absence of certain
functional groups (i.e. bond between O-H)
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IR easily detects –OH, -NH, -NO2
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Especially useful for detecting and distinguishing among C=O
containing compounds
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Liquid, solid or gas samples
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Rapid scanners linked to computers
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IR Instrument
Sample
Compartment
IR Source
Detector
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An Infrared Spectrometer
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Regions of the Infrared Spectrum
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IR region is lower in photon energy than visible light
(below red – produces heating as with a heat lamp)
IR radiation – just outside visible light 400 –800 nm
(infra red)
Wave length  2,500 nm – 16,700 nm
Energy: 0.1 – 35 kcal/mol causes molecular vibrations
IR energy in a spectrum is usually measured as
wavenumber (cm-1), the inverse of wavelength and
proportional to frequency (Wavenumber (cm-1) =
1/l(cm))
so IR Spectrum range: 600 – 4,000 cm-1
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Regions of the Infrared Spectrum
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4000-2500 cm-1 N-H, C-H, O-H (stretching)
 3300-3600 N-H, O-H
 3000 C-H
2500-2000 cm-1 CºC and C º N (stretching)
2000-1500 cm-1 double bonds (stretching)
 C=O 1680-1750
 C=C 1640-1680 cm-1
Below 1500 cm-1 “fingerprint” region
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Fingerprint of Molecule
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Whole-molecule vibrations and bending
vibrations are also quantitized.
No two molecules will give exactly the
same IR spectrum (except enantiomers).
Simple stretching: 1600-3500 cm-1.
Complex vibrations: 600-1400 cm-1,
called the “fingerprint region.”
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IR Table
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Tables of values
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Absorption Spectra
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Molecules - 3 types of Spectral Energy
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Electronic Energy (UV/Vis)
Absorption or emission in ultraviolet and visible
 region (27,000 cm-1 to 13,000 cm-1)
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Rotational Energy (microwave)
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Absorption in far infrared region (400 cm-1 to 50
cm-1)
Vibrational Energy (infrared)
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Absorption in near, mid, and far infrared region
(12,800 cm-1 to 50 cm-1)
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Infrared Energy Modes
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IR energy absorption corresponds to specific
modes, corresponding to combinations of atomic
movements, such as bending and stretching of
bonds between groups of atoms called “normal
modes”
Energy is characteristic of the atoms in the
group and their bonding
Corresponds to vibrations and rotations
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Vibrational modes leading to IR absorptions:
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How to Prepare IR Liquid sample
IR transparent Salt Plates
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Continued IR sample
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Continued IR sample
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Continued IR sample
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Continued IR sample
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Continued IR sample
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Continued IR sample
Light Path
(shown by red line)
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Solid samples
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Continued IR sample
Click Here to Start Scan
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Continued IR sample
Sample of a
printout of
an IR
spectrum.
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FT-IR Spectrometer
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Uses an interferometer.
Has better sensitivity.
Less energy is needed from source.
Completes a scan in 1-2 seconds.
Takes several scans and averages them.
Has a laser beam that keeps the
instrument accurately calibrated.
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References
http://eu.wikipedia.org/wiki/infraredSpectroscopy
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Separation sciences research and development
chapter 15
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Introduction to spectroscopy
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The Guide for student of organic chemistry D.Pavia
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Modern in Infrared spectoscopy D.parpara stiwart
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Skooge for instrumental analysis D.skooge
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Thank You
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