||Chapter 13: Spectroscopy
H-NMR Chemical shifts
- The chemical shift is the position on the
δ scale (in ppm) where the peak occurs.
- Typical δ /ppm values for protons in different chemical environments
are shown in the schematic figure below.
- There are two major factors that influence chemical shifts
(a) deshielding due to reduced
electron density (due electronegative atoms) and
(b) anisotropy (due to magnetic fields
generated by π bonds).
Note that the figure shows the typical chemical shifts for protons being
influenced by a single group.
In cases where a proton is influenced by more than one group, the effects
are essentially cumulative.