3.15 NMR

• What does each peak in a carbon nmr show?

  Eah set of equivelent carbons
• How do you find equivalent carbon atoms?

  If the carbon has unique 4 bonds (including what's attached to each bond)
• What does each peak in hydrogen nmr show?

  Each set of equivalent hydrogen atoms. The taller the peak the more equivalent H atoms there are.
• How do you find equivalent hydrogen atoms?

  The amount of hydrogens bonded to the atom that is bonded to the original hydrogen.
• What does the appearance (singlet, doublet, triplet) mean on peaks of H NMR?

  The number of H atoms +1 bonded to the molecule that is originally bonded to the H
• What do hydrogens bonded to oxygen or nitrogen appear as on the spectrum of H NMR?

  Singlets
• What solvent is used for non molecules and why?

  CCl4 because it has no hydrogens so will not show on that spectra and we know where the peak on the C NMR will be.
• What solvent is used for polar molecules and why?

  CDCl3 because it has no hydrogens so will not show on that spectra and we know where the peak on the C NMR will be.
• What is used to calibrate nmr spectrums?

  TMS tetramethylsilane Si(CH3)4
• Why is TMS used?

  its signal is away from all the others

  
  

  it only gives one signal

  
  

  it is non-toxic

  
  

  it is inert

  
  

  it has a low boiling point and so can be removed from sample easily
• What is meant by chemical shift? What's the unit?

  Distance of peaks from TMS standard.

  
  

  Measured in ppm.
• What determines chemical shift?

  The precense of electronegative atoms

  
  

  which reduces shielding

  
  

  causing greater chemical shift
• If splitting pattern is mentioned, what is it referring to?

  Singles, doubles, triplets