|Chapter 13: Spectroscopy|
|The chemical shift in absolute terms is defined by the frequency
of the resonance expressed with reference to a standard compound which is
defined to be at 0 ppm. The scale is made more manageable by expressing
it in parts per million (ppm) and is indepedent of the spectrometer
It is often convienient to describe the relative positions of the resonances in an NMR spectrum. For example, a peak at a chemical shift, δ, of 10 ppm is said to be downfield or deshielded with respect to a peak at 5 ppm, or if you prefer, the peak at 5 ppm is upfield or shielded with respect to the peak at 10 ppm. The terms shielded and deshielded will be explained later.
|© Dr. Ian Hunt, Department of Chemistry|