11

University of Petra Faculty of Science & Arts Department of Chemistry

Seminar

I.R SpectroscopyBy

Firas Al-ouzeh

Supervisor : Nuha I. SwidanSummer 2007

22

- -What is spectroscopyWhat is spectroscopy??

- -Electromagnetic spectrumElectromagnetic spectrum. .

- -IR active and inactiveIR active and inactive. .

- -Infrared spectroscopyInfrared spectroscopy. .

- -IR instrumentIR instrument..

- -Region of infrared spectrumRegion of infrared spectrum

- -Fingerprint moleculeFingerprint molecule..- - -IR tableIR table..

- - -Infrared energy modeInfrared energy mode..

Outline

33

---Vibration modes leading to IR Vibration modes leading to IR absorptionabsorption..

- - -How to prepare IR sampleHow to prepare IR sample..- - -FT-IR spectrometerFT-IR spectrometer..

- - -ReferencesReferences

Outline

44

What is SpectroscopyWhat is Spectroscopy?? Shine light (energy) on a sample to Shine light (energy) on a sample to

determine what is insidedetermine what is inside Measure the amount of Measure the amount of

electromagnetic radiation electromagnetic radiation absorbed and/or emitted by a absorbed and/or emitted by a compound compound

Different molecules absorb at Different molecules absorb at different energiesdifferent energies

55

Electromagnetic SpectrumElectromagnetic SpectrumEach form of spectroscopy uses a different Each form of spectroscopy uses a different

part of the electromagnetic spectrumpart of the electromagnetic spectrum

66

IR-Active and InactiveIR-Active and Inactive

A polar bond is usually IR-active.A polar bond is usually IR-active. A nonpolar bond in a symmetrical A nonpolar bond in a symmetrical

molecule will absorb weakly or not at all.molecule will absorb weakly or not at all.

=>

77

Infrared SpectroscopyInfrared Spectroscopy Evaluates covalent bond stretchingEvaluates covalent bond stretching

Infrared (IR) spectroscopy measures the bond vibration Infrared (IR) spectroscopy measures the bond vibration frequencies in a molecule and is used to determine the frequencies in a molecule and is used to determine the functional group.functional group.

IR spectra allow one to determine the presence or absence IR spectra allow one to determine the presence or absence of certain of certain functional groups functional groups (i.e. bond between O-H(i.e. bond between O-H))

IR easily detects IR easily detects –OH, -NH, -NO–OH, -NH, -NO22

Especially useful for detecting and distinguishing among Especially useful for detecting and distinguishing among C=OC=O containing compounds containing compounds

Liquid, solid or gas samplesLiquid, solid or gas samples

Rapid scanners linked to computersRapid scanners linked to computers

88

IR InstrumentIR InstrumentSample Sample

CompartmentCompartmentIR SourceIR Source DetectorDetector

99

An Infrared SpectrometerAn Infrared Spectrometer

=>

1010

IR region is lower in photon energy than visible IR region is lower in photon energy than visible light (below red – produces heating as with a light (below red – produces heating as with a heat lamp)heat lamp)

IR radiation – just outside visible light 400 –800 IR radiation – just outside visible light 400 –800 nm (infra red)nm (infra red)

Wave length Wave length 2,500 nm – 16,700 nm 2,500 nm – 16,700 nm Energy: 0.1 – 35 kcal/mol causes molecular Energy: 0.1 – 35 kcal/mol causes molecular

vibrationsvibrations IR energy in a spectrum is usually measured as IR energy in a spectrum is usually measured as

wavenumber (cm-1), the inverse of wavelength wavenumber (cm-1), the inverse of wavelength and proportional to frequency (Wavenumber (cm-and proportional to frequency (Wavenumber (cm-1) = 1/l(cm))1) = 1/l(cm))

so IR Spectrum range: 600 – 4,000 cmso IR Spectrum range: 600 – 4,000 cm-1-1

Regions of the Infrared Regions of the Infrared SpectrumSpectrum

1111

Regions of the Infrared Regions of the Infrared SpectrumSpectrum

4000-2500 cm4000-2500 cm-1-1 N-H, C-H, O-H (stretching) N-H, C-H, O-H (stretching) 3300-3600 N-H, O-H3300-3600 N-H, O-H 3000 C-H3000 C-H

2500-2000 cm2500-2000 cm-1-1 C CC and C C and C N N (stretching)(stretching) 2000-1500 cm2000-1500 cm-1-1 double bonds (stretching) double bonds (stretching)

C=O 1680-1750C=O 1680-1750 C=C 1640-1680 cmC=C 1640-1680 cm-1-1

Below 1500 cmBelow 1500 cm-1-1 “fingerprint” region “fingerprint” region

1212

Fingerprint of MoleculeFingerprint of Molecule

Whole-molecule vibrations and bending Whole-molecule vibrations and bending vibrations are also quantitized.vibrations are also quantitized.

No two molecules will give exactly the No two molecules will give exactly the same IR spectrum (except enantiomers).same IR spectrum (except enantiomers).

Simple stretching: 1600-3500 cmSimple stretching: 1600-3500 cm-1-1.. Complex vibrations: 600-1400 cmComplex vibrations: 600-1400 cm-1-1, called , called

the “fingerprint region.”the “fingerprint region.” =>=>

1313

IR TableIR Table Tables of valuesTables of values

1414

Absorption SpectraAbsorption Spectra Molecules - 3 types of Spectral EnergyMolecules - 3 types of Spectral Energy

Electronic Energy (Electronic Energy (UVUV/Vis)/Vis) Absorption or emission in ultraviolet and Absorption or emission in ultraviolet and

visible visible region (27,000 cm-1 to 13,000 cm-1)region (27,000 cm-1 to 13,000 cm-1)

Rotational EnergyRotational Energy (microwave)(microwave) Absorption in far infrared region (400 cm-1 to Absorption in far infrared region (400 cm-1 to

50 cm-1)50 cm-1) Vibrational Energy (infrared)Vibrational Energy (infrared)

Absorption in near, mid, and far infrared region Absorption in near, mid, and far infrared region (12,800 cm-1 to 50 cm-1)(12,800 cm-1 to 50 cm-1)

1515

Infrared Energy ModesInfrared Energy Modes

IR energy absorption corresponds to IR energy absorption corresponds to specific modes, corresponding to specific modes, corresponding to combinations of atomic movements, such combinations of atomic movements, such as bending and stretching of bonds as bending and stretching of bonds between groups of atoms called “normal between groups of atoms called “normal modes”modes”

Energy is characteristic of the atoms in the Energy is characteristic of the atoms in the group and their bondinggroup and their bonding

Corresponds to Corresponds to vibrationsvibrations and rotations and rotations

1616

Vibrational modes leading to IR absorptions:

1717

How to Prepare IR Liquid sampleHow to Prepare IR Liquid sample

IR transparent Salt PlatesIR transparent Salt Plates

1818

Continued IR sampleContinued IR sample

1919

Continued IR sampleContinued IR sample

2020

Continued IR sampleContinued IR sample

2121

Continued IR sampleContinued IR sample

2222

Continued IR sampleContinued IR sample

2323

Continued IR sampleContinued IR sample

Light PathLight Path(shown by red line)(shown by red line)

2424

Solid samplesSolid samples

2525

Continued IR sampleContinued IR sample

Click Here to Start ScanClick Here to Start Scan

2626

Continued IR sampleContinued IR sample

Sample of a Sample of a printout of printout of an IR an IR spectrum.spectrum.

2727

FT-IR SpectrometerFT-IR Spectrometer

Uses an interferometer.Uses an interferometer. Has better sensitivity.Has better sensitivity. Less energy is needed from source.Less energy is needed from source. Completes a scan in 1-2 seconds.Completes a scan in 1-2 seconds. Takes several scans and averages them.Takes several scans and averages them. Has a laser beam that keeps the Has a laser beam that keeps the

instrument accurately calibrated. instrument accurately calibrated. =>=>

2828

ReferencesReferences http://eu.wikipedia.org/wiki/infrared-http://eu.wikipedia.org/wiki/infrared-SpectroscopySpectroscopy Separation sciences research and development Separation sciences research and development

chapter 15chapter 15 Introduction to spectroscopyIntroduction to spectroscopy The Guide for student of organic chemistry The Guide for student of organic chemistry

D.PaviaD.Pavia Modern in Infrared spectoscopy D.parpara stiwartModern in Infrared spectoscopy D.parpara stiwart

Skooge for instrumental analysis D.skooge Skooge for instrumental analysis D.skooge

2929

Thank You