3.3.6.3 Infrared spectroscopy

• The fingerprinting region is the region between 1500-1400cm-1. It can be used to identify an unknown sample by comparing to a database of known compound spectra. 
• Explain how infrared spectroscopy can be used to show that an aldehyde is definitely pentanal (2)

  • compare spectrum of aldehyde with known spectrum of pentanal
  • there should be an exact match
• Infrared spectroscopy can be used to identify functional groups because bonds absorb infrared radiation at different characteristic wavenumbers.
• Alcohols (-OH) produce a broad peak on an IR spectrum.
• Aldehydes (C=O) produce a sharp peak on an IR spectrum.
• Carboxylic acids (COOH) produce both a broad peak and sharp peak on an IR spectrum.
• The atmosphere consists of greenhouse gases such as carbon dioxide, methane, water vapour and other gases that absorb the infra-red radiation and keep the earth warm. This effect is called as green house effect. 
• Due to increase in burning of fossil fuels over years, the amount of pollutants in the atmosphere is increasing. These pollutants contribute to the greenhouse effect by absorbing infra-red radiation. 
• The C=O, O-H and C-H bonds in carbon dioxide, water and methane respectively absorb infra-red radiations, which contribute to global warming.