BRAINCAKEChemical Shift
The position of an NMR signal is given as its chemical shift, δ, measured in parts per million (ppm) relative to a reference compound.
The reference is tetramethylsilane (TMS), Si(CH3)4, defined as δ = 0. TMS is used because all 12 of its hydrogen atoms (and all 4 carbon atoms) are in the same environment, so it gives a single sharp peak; this peak is at a lower chemical shift than almost all organic compounds; and it is inert, non-toxic and volatile, so it is easily removed afterwards.
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All 15 lessons in Modern Analytical Techniques · All Edexcel A-level Chemistry topics