BRAINCAKEChemical Shift
The position of an NMR peak is given by its chemical shift, symbol δ, measured in parts per million (ppm). The chemical shift is measured relative to a reference compound, which is given δ = 0 ppm.
Chemical shift depends on the chemical environment of the nucleus. The electrons around a nucleus shield it from the external magnetic field.
• A nucleus near an electronegative atom (O, N, Cl, Br) or a C=O group has electron density pulled away from it. It is deshielded and has a larger chemical shift.
• A nucleus surrounded only by C and H is more shielded and has a smaller chemical shift.
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More in NMR Spectroscopy
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All 12 lessons in NMR Spectroscopy · All OCR A-level Organic Chemistry topics