1 University of Petra Faculty of Science & Arts Department of Chemistry Seminar I.R Spectroscopy By Firas Al-ouzeh Supervisor : Nuha I. Swidan Summer 2007

2 - What is spectroscopy? - Electromagnetic spectrum. - IR active and inactive. - Infrared spectroscopy. - IR instrument. - Region of infrared spectrum - Fingerprint molecule. - - IR table. - - Infrared energy mode. Outline

3 - -Vibration modes leading to IR absorption. - - How to prepare IR sample. - - FT-IR spectrometer. - - References Outline

4 What is Spectroscopy? Shine light (energy) on a sample to determine what is inside Shine light (energy) on a sample to determine what is inside Measure the amount of electromagnetic radiation absorbed and/or emitted by a compound Measure the amount of electromagnetic radiation absorbed and/or emitted by a compound Different molecules absorb at different energies Different molecules absorb at different energies

5 Electromagnetic Spectrum Each form of spectroscopy uses a different part of the electromagnetic spectrum Each form of spectroscopy uses a different part of the electromagnetic spectrum

6 IR-Active and Inactive A polar bond is usually IR-active. A polar bond is usually IR-active. A nonpolar bond in a symmetrical molecule will absorb weakly or not at all. A nonpolar bond in a symmetrical molecule will absorb weakly or not at all. =>

7 Infrared Spectroscopy Evaluates covalent bond stretching Evaluates covalent bond stretching Infrared (IR) spectroscopy measures the bond vibration frequencies in a molecule and is used to determine the functional group. Infrared (IR) spectroscopy measures the bond vibration frequencies in a molecule and is used to determine the functional group. IR spectra allow one to determine the presence or absence of certain functional groups (i.e. bond between O-H) IR spectra allow one to determine the presence or absence of certain functional groups (i.e. bond between O-H) IR easily detects – OH, -NH, -NO 2 IR easily detects – OH, -NH, -NO 2 Especially useful for detecting and distinguishing among C=O containing compounds Especially useful for detecting and distinguishing among C=O containing compounds Liquid, solid or gas samples Liquid, solid or gas samples Rapid scanners linked to computers Rapid scanners linked to computers

8 IR Instrument Sample Compartment IR Source Detector

9 An Infrared Spectrometer =>

10 IR region is lower in photon energy than visible light (below red – produces heating as with a heat lamp) 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) IR radiation – just outside visible light 400 – 800 nm (infra red) Wave length 2,500 nm – 16,700 nm Wave length 2,500 nm – 16,700 nm Energy: 0.1 – 35 kcal/mol causes molecular vibrations 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)) 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 so IR Spectrum range: 600 – 4,000 cm -1 Regions of the Infrared Spectrum

11 Regions of the Infrared Spectrum cm -1 N-H, C-H, O-H (stretching) cm -1 N-H, C-H, O-H (stretching) N-H, O-H N-H, O-H 3000 C-H 3000 C-H cm -1 C º C and C º N (stretching) cm -1 C º C and C º N (stretching) cm -1 double bonds (stretching) cm -1 double bonds (stretching) C=O C=C cm -1 Below 1500 cm -1 “fingerprint” region Below 1500 cm -1 “fingerprint” region

12 Fingerprint of Molecule Whole-molecule vibrations and bending vibrations are also quantitized. Whole-molecule vibrations and bending vibrations are also quantitized. No two molecules will give exactly the same IR spectrum (except enantiomers). No two molecules will give exactly the same IR spectrum (except enantiomers). Simple stretching: cm -1. Simple stretching: cm -1. Complex vibrations: cm -1, called the “ fingerprint region. ” => Complex vibrations: cm -1, called the “ fingerprint region. ” =>

13 IR Table Tables of values

14 Absorption Spectra Molecules - 3 types of Spectral Energy Electronic Energy (UV/Vis) Absorption or emission in ultraviolet and visible region (27,000 cm-1 to 13,000 cm-1) Rotational Energy(microwave) Absorption in far infrared region (400 cm-1 to 50 cm-1) Vibrational Energy (infrared) Absorption in near, mid, and far infrared region (12,800 cm-1 to 50 cm-1)

15 Infrared Energy Modes 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 ” 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 Energy is characteristic of the atoms in the group and their bonding Corresponds to vibrations and rotations Corresponds to vibrations and rotationsvibrations

16 Vibrational modes leading to IR absorptions :

17 How to Prepare IR Liquid sample IR transparent Salt Plates

18 Continued IR sample

19 Continued IR sample

20 Continued IR sample

21 Continued IR sample

22 Continued IR sample

23 Continued IR sample Light Path (shown by red line)

24 Solid samples

25 Continued IR sample Click Here to Start Scan

26 Continued IR sample Sample of a printout of an IR spectrum.

27 FT-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 instrument accurately calibrated. => Has a laser beam that keeps the instrument accurately calibrated. =>

28 References Spectroscopy Separation sciences research and development Separation sciences research and development chapter 15 Introduction to spectroscopy Introduction to spectroscopy The Guide for student of organic chemistry D.Pavia The Guide for student of organic chemistry D.Pavia Modern in Infrared spectoscopy D.parpara stiwart Modern in Infrared spectoscopy D.parpara stiwart Skooge for instrumental analysis D.skooge Skooge for instrumental analysis D.skooge

29 Thank You