Mr. Strickland's Chemistry     pi-sigma

Topic 11.3

Essential idea: Analytical techniques can be used to determine the structure of a compound, analyze the composition of a substance or determine the purity of a compound. Spectroscopic techniques are used in the structural identification of organic and inorganic compounds.


  • The degree of unsaturation or index of hydrogen deficiency (IHD) can be used to determine from a molecular formula the number of rings or multiple bonds in a molecule.
  • Mass spectrometry (MS), proton nuclear magnetic resonance spectroscopy (1H NMR) and infrared spectroscopy (IR) are techniques that can be used to help identify compounds and to determine their structure.


Applications and skills:

  • Determination of the IHD from a molecular formula.
  • Deduction of information about the structural features of a compound from percentage composition data, MS, 1H NMR or IR.



  • The electromagnetic spectrum (EMS) is given in the data booklet in section 3. The regions employed for each technique should be understood.
  • The operating principles are not required for any of these methods.
  • The data booklet contains characteristic ranges for IR absorptions (section 26), 1H NMR data (section 27) and specific MS fragments (section 28). For 1H NMR, only the ability to deduce the number of different hydrogen (proton) environments and the relative numbers of hydrogen atoms in each environment is required. Integration traces should be covered but splitting patterns are not required.



  • Monitoring and analysis of toxins and xenobiotics in the environment is a continuous endeavor that involves collaboration between scientists in different countries.


Theory of knowledge:

  • Electromagnetic waves can transmit information beyond that of our sense perceptions. What are the limitations of sense perception as a way of knowing?



  • IR spectroscopy is used in heat sensors and remote sensing in physics.
  • Protons in water molecules within human cells can be detected by magnetic resonance imaging (MRI), giving a three-dimensional view of organs in the human body.