Basic principle of IR spectroscoy
- 1. Presented by: Md. Faysal Ah ID:151-29-760 Sec: B 13th DIU
- 2. Spectroscopy • Method of “Seeing the “unseeable” • Using electromagnetic radiation to obtain information about atoms and molecules that are too small to see. atoms molecule
- 3. IR spectroscopy IR spectroscopy is the spectroscopic technique which uses the Infrared light and studies its interaction with the molecules. The spectra generated can give a lot of information about the molecule, especially about the functional groups associated.
- 4. Basics of IR spectrophotometer Wave number = 1 Wavelength in centimeters
- 5. In the IR spectroscopy, the absorbed energy brings about predominant changes in the vibrational energy which depends upon three things. i) Masses of the atoms present in a molecule, ii) Strength of the bonds iii) The arrangement of atoms within the molecule.
- 6. Instrumentation of IR spectrophotometer:
- 7. Instrumentation of IR spectrophotometer:
- 11. When energy in the form of infrared radiation is applied then it causes the vibration between the atoms of the molecules and when, Applied infrared frequency = Natural frequency of vibration Then, Absorption of IR radiation takes place and a peak is observed. Different functional groups absorb characteristic frequencies of IR radiation. Hence gives the characteristic peak value. Therefore, IR spectrum of a chemical substance is a finger print of a molecule for its identification.
- 12. Criteria for a compound to absorb IR radiation 1. Correct wavelength of radiation 2. Change in dipole moment 1. Correct wavelength of radiation: A molecule to absorb IR radiation, the natural frequency of vibrations of some part of a molecule is the same as the frequency of incident radiation.
- 13. 2. Change in dipole moment : • A molecule can only absorb IR radiation when its absorption cause a change in its electric dipole. • A molecule is said to have an electric dipole when there is a slight positive and a slight negative charge on its component of atoms.
- 14. Molecular vibrations There are 2 types of vibrations: 1.Stretching vibrations 2.Bending vibrations 1. Stretching vibrations: Occurs at higher energy: 4000-1250 cm-1 2 types: a) Symmetrical stretching b)Asymmetrical stretching
- 16. 2. Bending vibrations The positions of the atom change with respect to the original bond axis. Occurs at low energy: 1400-666 cm-1 . • There are 2 types: a) In plane bending: scissoring, rocking b) Out plane bending: wagging, twisting
- 18. • IR region: 0.8 µm (800nm) to 1000 µm (1mm) Sub divided into 1.Near IR: 0.8-2 µm 2.Middle IR: 2-15 µm 3.Far IR: 15-1000 µm Most of the analytical applications are confined to the middle IR region because absorption of organic molecules are high in this region.