3.3.6.3 Infrared spectroscopy

• What is infrared specto used for?

  Analytical technique used to identify the functional groups withing molecules
• Infrared radiation and molecules

  All molecules absorb IR light, IR light makes the bonds in a molecule vibrate, occurs in 2 ways
• What does IR light do

  Makes the bonds vibrate
• Name the 2 ways vibration can occur

  Stretching or bending
• What does each bond vibrations depend on


  Bond strength, bond length and mass of atom at either end of the bond
• What does the spectrum give us?

  Peaks
• What are peaks caused by

  Absorbance troughs
• Each peak is

  Characteristic to a specific bond/ atoms
• How are these troughs created?

  Frequency of IR light being absorbed from a bond vibrating bond
• What is on the x-axis

  Wavenumber
• What is on the y-axis

  Transmittance %
• Between 1500-500 is called the

  Fingerprint region
• What is the fingerprint region?

  Region of absorbance between 500-1,500, it is unique for each molecule
• Most organic molecules contain the 2,900cm

  C-H bond