Chemical Shift Definition:
In an NMR spectrum, the location of a signal, defined relative to the frequency of absorption of a reference compound, tetramethylsilane (TMS).
Chemical Shift Explained:
Several important features should be noted when talking about chemical shifts.
- When reading chemical shifts in NMR spectroscopy, it is showing the location of a resonating proton that has taken up radiation.
- Chemical shifts are dimensionless, and have the accompanying unit, ppm (parts per million). The spectrum usually shows absorptions of protons between 0 and 12 ppm.
- Hint: When deducing information from a NMR spectroscopy, relative to chemical shift, most organic compounds have recorded units, thus a high intensity of protons around a certain region on the spectroscopy will correspond to the observed organic compound. Benzene’s protons are somewhere around 7.2 ppm, thus if you are reading a spectroscopy, and find a great deal of protons in that region, you can be fairly certain that the compound is or contains Benzene.