Infrared spectroscopy

• Infra-red radiation is heat absorbed by certain groups in a molecule at characteristic frequencies causing them to stretch depending on bond strength
• Frequencies:

  C-H: Always around 3000, in saturated they are below 3000 in unsaturated they are above 3000

  CH in aldehydes is around 2700
• Frequencies:

  O-H: Often a very broad curve

  In carboxyl groups they are centred around 2500-3000

  In alcohols they are centred around 3500-3200( more curve)
• Frequencies:

  C=O: Aldehydes, ketones, carboxylic acids and esters all have this at a region of 1700
• Frequencies:

  C=C: Alkenes contain a small sharp peak around the region 1650