Carbon-13 NMR
Chemistry: IB Diploma Higher Level, topic 7.3.2
C13 NMR
The first type of NMR we shall look at is 13C NMR. This is slightly more simple than 1H NMR.
13C spectra
- We can work out the different 13C environments from the 13C spectra.
- In the spectra, different chemical shifts represent 13Cs in different environments.
- Remember it is only the isotope 13C that this NMR works for, NOT the more common 12C.
- 13C's abundance is only 1.1%.
Tetramethylsilane
- Tetramethylsilane (TMS) is used during the 13C spectrum readings as a reference.
- This is used because the chemical shifts along the x-axis are relative to the shift of TMS.
- TMS is a good reference since it only produces one peak at 0ppm because each 13C is in the same environment.
- For this reason, lots of spectra will have a single peak at 0ppm. Remember this is just your reference peak.
,w_800.png)
13C example
- 13C NMR of ethanal. You need to look at a data table to determine the carbon environments represented by the peaks in the spectrum.
- The peak at 200 ppm represents the carbon in the C=O bond.
- The peak at 31 ppm represents the carbon in the C-C bond.
- The peak at 0 ppm is the reference peak from TMS.
Test yourself on Carbon-13 NMR
In a 13C spectrum, there are 4 peaks. How many 1H environments do the peaks represent?