Fourier transform infrared spectroscopy[FTIR] Lec.12

Introduction FTIR is an effective analytical instrument for detecting functional groups and characterizing covalent bonding information.  FTIR testing identifies chemical compounds in consumer products, paints, polymers, coatings, pharmaceuticals, foods and other products. Organic molecules are flexible, atoms and groups of atoms can rotate about single covalent bonds. In addition, covalent bonds can stretch and bend as if their atoms were joined by flexible springs. Infrared spectroscopy, also called IR spectroscopy, probes stretching and bending vibrations of organic molecules.

Fourier Transform Infrared Spectroscopy (FTIR) identifies chemical bonds in a molecule by producing an infrared absorption spectrum.

How to read the curve? The horizontal axis at the bottom of the chart paper is calibrated in frequency (wavenumbers, cm-1); that at the top is calibrated in wavelength (micrometers, mm). The frequency scale is often divided into two or more regions. For all spectra reproduced in this text, the scale is divided into three linear regions: 4000–2200 cm-1,2200–1000 cm-1, and 1000–400 cm-1. The vertical axis measures transmittance %(the fraction of light transmitted), with 100%at the top and 0% at the bottom. According to the frequency range , we can determine the type of bond or the functional group. Each functional group or bond has range of frequency as shown in the next tables:

Examples: