TMS is Superior to Residual C H Cl 3 for Use as the Internal Reference for Routine 1 H NMR Spectra Recorded in CDCl 3 .

Tetramethylsilane was recommended for use as an internal reference compound in proton NMR spectroscopy over 60 years ago. However, it is a common practice that researchers reference the analyte chemical shifts to the residual proton resonance in the deuterated solvent in which the spectrum is recorded. Because CDCl 3 is the most commonly used NMR solvent for routine analysis of organic compounds, the effect of various functional groups on the CHCl 3 resonance is important. Described here are results that show why referencing spectra to TMS rather than CHCl 3 in CDCl 3 results in more accurate chemical shifts and should be the recommended practice. Simultaneous measurement of separate compartments of unperturbed CDCl 3 /TMS vis-à-vis CDCl 3 /TMS/solute solutions using a concentric tube arrangement was key. This study is reported in this venue because the audience/readership is quite appropriate and is, hopefully, both receptive to and appreciative of the guidance provided.