nuclear magnetic resonance spectroscopy

• What is NMR spectroscopy used for?


  It is used to determine the structure of a molecule.
• How does NMR spectroscopy analyze a molecule?


  By analyzing the energy of each bond environment.
• What does the presence of different peaks in an NMR spectrum indicate?


  It indicates different bond environments within a molecule.
• What standard molecule is used in NMR spectroscopy?


  Tetramethylsilane (TMS).
• Why is TMS considered a standard molecule in NMR?

  Because it contains four identical carbon and hydrogen environments.
• At what value does TMS appear on the NMR spectrum?


  At ∂=0 ppm.
• What does C¹³ NMR analyze?


  It analyzes the different carbon environments in a molecule.
• What happens to the ∂ values of carbon environments near oxygen?


  They are shifted to the right.
• Why do molecules with symmetry display fewer ∂ peaks?


  Because they have identical environments that absorb the same energy.
• How many peaks would you expect in the NMR spectrum of 1,2-cyclohexanediol?


  Three peaks.
• Where can you find the C¹³ NMR ∂ shift values?


  On the AQA Chemistry Data Sheet.
• What does H¹ NMR analyze?


  It analyzes the different hydrogen environments in a molecule.
• Why must samples for H¹ NMR be dissolved in a non-hydrogen-containing solvent?


  To prevent producing additional ∂ peaks on the spectrum.
• What is a common solvent used in H¹ NMR?


  CCl₄.
• How do the heights of peaks in H¹ NMR spectra relate to the molecule?


  They correspond to the relative intensity of each ∂ value, indicating the number of hydrogens in that environment.
• What does the splitting pattern of peaks in H¹ NMR indicate?


  It indicates the number of hydrogens on the adjacent carbon atom.
• What is the ‘n+1’ rule in NMR spectroscopy?


  It states that the number of peaks in a splitting pattern is one more than the number of hydrogens on the adjacent carbon.
• What are the splitting patterns in H¹ NMR and their meanings?


  • Singlet: no H on adjacent carbon
  • Doublet: 1 H on adjacent carbon
  • Triplet: 2 H on adjacent carbon
  • Quartet: 3 H on adjacent carbon
• What is a common splitting pattern that helps in deciphering molecular structure?

  A triplet-quartet splitting pattern represents a -CH₂-CH₃ fragment.
• How can multiple fragments be used in NMR analysis?


  They can be pieced together to determine the full molecule structure.