1. Infrared SpectroscopyIR
Dr. Wael Abu-Dayyih

2. Introduction
Mass spectroscopy === Molecular formula Infrared spectroscopy === Functional groups UV spectroscopy === Extent of conjugation NMR spectroscopy === Map of C-H framework

3. Introduction All molecules have a certain amount of energy
(quantized) and are in constant motion
stretching
Scissoring
Twisting

4. Introduction

5. Introduction

6. Theory
exploits the fact that molecules absorb specific frequencies that are characteristic of their structure

7. Theory
The result of this energy absorption is an increased amplitude for the vibration

8. Molecular Motion Translational movement Rotational movement
Vibrational movement

9. Theory In vibrational motion : Each atom has three degrees of freedom
For molecules with N atoms in them, linear molecules have 3N – 5 degrees of vibrational modes, whereas nonlinear molecules have 3N – 6 degrees of vibrational modes

10. Theory
Carbon dioxide has 3 x = 4 vibrations

11. Interpreting the spectra
IR spectra are obtained by detecting changes in transmittance (or absorption) intensity
as a function of frequency
Most commercial instruments separate and measure IR radiation using dispersive
spectrometers or Fourier transform spectrometers

12. Example
Toluene

13. Example

14. Sample preparation
It is possible to obtain an IR spectrum from samples in many different forms, such as liquid, solid, and gas .