BRAINCAKEChemical Shift
In an NMR spectrum, the position of a peak is given by its chemical shift, symbol δ, measured in parts per million (ppm). It compares the absorption frequency of a nucleus with that of a reference compound, which is set at δ = 0.
Chemical shift depends on the molecular environment of the nucleus. Electrons around a nucleus shield it from the applied magnetic field. When an electronegative atom such as O, N or a halogen is nearby, it pulls electron density away. The nucleus is deshielded and absorbs at a higher chemical shift. So the closer a carbon or hydrogen is to an electronegative atom or a C=O group, the larger its δ value.
Sign in free to see the rest of this lesson, the R.E.C.I.P.E. recall steps and the quiz
BrainCake is free. Make an account in seconds and pick up where this page stops.
More in NMR Spectroscopy
- Nuclear Magnetic Resonance
- The TMS Standard
- Deuterated Solvents
- 13C NMR Spectroscopy
- Interpreting 13C NMR Spectra
- 1H NMR Spectroscopy
- Integration Traces
- Spin-Spin Splitting
All 11 lessons in NMR Spectroscopy · All AQA A-level Chemistry topics