Topic 15 Nuclear mag spec

• What is C13 NMR? [2]

  Provides data about the carbon skeleton in a molecule

  Number of non equivalent carbon atoms (environments)= number of peaks
• What is a reference peak for C13 NMR[2]

  Tetra methyl silane (TMS)

  produces one peak- all carbon atoms are in the same environment

  Peak is at the PHS due to a very low electronegativity of silicon
• How does the spectrometer work? [2]

  MAchine needs to be calibrated by TMS for reference peak

  need to dissolve sample in solvent- two options: Cl4 or CDCl3
• Why do you use Cl4 as a solvent? [2]

  There is no permanent dipole and so is used for non polar compounds
• Why do you use CDCl3 as a solvent? [2]

  Has a permanent dipole and so is used for polar compounds
• In proton NMR size matters
• What is the N+1 rule? [1]

  N= number of neighbouring hydrogen atoms + 1
• Singlet is caused by 0 hydrogens

  doublet is caused by 1 hydrogen

  triplet is caused by 2 hydrogens

  quartet is caused by 3 hydrogens
• What are the cases where the N+1 rule doesn’t apply? [1]

  Symmetrical molecules means the rule doesn’t apply
• What is another name for the n+1 rule? [1]

  Spin spin coupling