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Mass spectra and infrared spectroscopyEdexcel International A Level Chemistry: Flashcards

What these 14 flashcards ask

  • What is the molecular ion peak?
  • What is the base peak?
  • What does a peak at M − 15 show?
  • What does a peak at M − 17 show?
  • Which ion gives m/z 15?
  • Which ion gives m/z 29?
  • Which ion gives m/z 43 in a ketone such as propanone?
  • In IR, in which range does C=O absorb?
  • In IR, in which range does the O–H of an alcohol absorb?
  • How does the O–H absorption of a carboxylic acid differ?
  • Where does C=C absorb in the IR spectrum?
  • Where does the aldehyde C–H absorb?
  • What does an N–H bond in an amine absorb at?
  • How do you tell a carboxylic acid from an alcohol using IR?

Exam questions on Mass spectra and infrared spectroscopy

  1. A compound X contains carbon, hydrogen and oxygen only. Its mass spectrum has a molecular ion peak at m/z 58, the largest fragment peak at m/z 43, a small peak at m/z 15 and no significant peak at m/z 29. Its infrared spectrum has a strong absorption at 1715 cm⁻¹ and no absorption above 3000 cm⁻¹.
    Give the formulae of the ions responsible for the peaks at m/z 43 and m/z 15.2 marks
  2. A liquid Z has an infrared spectrum with a very broad absorption between 2500 and 3300 cm⁻¹ and a strong, sharp absorption at 1710 cm⁻¹. Its molecular ion peak is at m/z 74.
    A student suggests that Z is an alcohol. Use the infrared data to explain why this is not correct.2 marks
  3. A compound W contains only carbon, hydrogen and oxygen. Its mass spectrum has peaks at m/z 74, 57, 45 and 29, with the peak at m/z 74 the molecular ion. Its infrared spectrum has a very broad absorption at 2500 to 3300 cm⁻¹ and a strong absorption at 1710 cm⁻¹.
    Use the infrared data to deduce the functional group in W and state the evidence for it.3 marks
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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).