Chapter 13: Spectroscopy

H-NMR Chemical shifts

• The chemical shift is the position on the d scale (in ppm) where the peak occurs.
• Typical d /ppm values for protons in different chemical environments are shown in the 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 p 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.