Answer / raees sayyed

You probably mean referencing the chemical shift scale (?) For NMR spectra you don't report absolute absorption frequencies but you reference them with respect to an internal standard. For 1H NMR spectra this internal standard is usually tetramethylsilane (TMS). You add a very small amount (ca. 0.03 per cent) of TMS to the solution to be measured (or you buy a solvent that already contains TMS) and report the peak positions of your compound relative to the TMS signal. I. e. TMS is the zero point of your chemical shift scale.

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