carbon-13 NMR spectroscopy

• a carbon-13 spectrum provides 2 important pieces of information about a molecule:

  • the number of different carbon environments - from the number of peaks
  • the types of carbon environment present - from the chemical shift
• the chemical shift is referenced against TMS at delta = 0ppm

  the chemical shift range of about 220ppm is sufficiently wide to separate carbon atoms that have only slightly different environments
• there are four main types of carbon atom that absorb over different chemical shift ranges:

  • carbon as part of c=o (170-220)
  • carbon as part of c=c or aromatic ring (110-150)
  • carbon bonded to an electronegative atom e.g. O, N, Cl, Br (40-90)
  • carbon bonded to carbon (0-40)
  • the chemical shifts may also be outside these ranges depending on the solvent, concentration and substituents