To avoid spectra dominated by the solvent signal, most 1H NMR spectra are recorded in a deuterated solvent. However, deuteration is never "100%", so signals for the residual protons are observed. In chloroform solvent (CDCl3), this corresponds to CHCl3, producing a singlet signal is observed at 7.26 ppm. For methanol solvent, this corresponds to CHD2OD, so a 1:2:3:2:1 pentet signal is observed at 3.31 ppm.
The same solvents are used for 13C NMR spectra, so the same rules about splitting patterns apply here also. The following table lists commonly used solvents and their chemical shifts, which are often used for frequency references. The chemical shift data is based on reference to the standard TMS (tetramethylsilane). It is a common practice to add TMS, or related compounds, as an internal reference standard for 1H and 13C NMR spectra with the proton signal occurring at 0.0 ppm and the carbon signal occurring at 0.0 ppm in the 13C NMR spectrum.
Common solvents are available in different degrees of deuteration. Signals for water occur at different frequencies in 1H NMR spectra depending on the solvent used. Listed below are the chemical shift positions of the water signal in several common solvents. Note that H2O is seen in aprotic solvents, while HOD is seen in protic solvents due to exchange with the solvent deuteriums.
* 2,2-Dimethyl-2-silapentane-5-sulfonic acid (DDS) is used in proton- and carbon-related NMR spectroscopy as a calibration standard, similar to tetramethylsilane (TMS), but with much higher water solubility. TMS is the most common NMR standard used in organic solvents such as chloroform or benzene. DSS or its sodium salt is required for proton experiments in water.
Common solvents are available in different degrees of deuteration.
