For D 2O as a solvent, the accepted reference peak (δ) 0) is the methyl signal of the sodium salt of 3-(trimeth- For example, the water peak in DMSO-d6 appears at nearly 3.33 ppm, but the same moisture peak in $\ce{CDCl3}$ appears at 1.56 ppm. * … What is the reason behind it? The chemical shifts were read and are presented in Table 1. However commercially available samples are not 100% pure and a residual DMSO-d5 H NMR signal is observed at 2.50ppm (quintet, JHD=1.9Hz). O peak at 3.3 ppm. I learned that dmso peak in 1H NMR caused by proton exchange. The C chemical shift of DMSO-d6 is 39.52ppm (septet). Note that the HOH and HOD peaks are separated in the spectrum. (Our NMR guy needed poorly deuterated DMSO for some studies, so I helped him to partially exchange the deuteriums for protons, by cooking it with NaOH.) Figure 2- 1H NMR spectrum of 5.3 mg of 2,6-di-tert-butyl-4-methylphenol in DMSO-d 6 with 100 ppm D 2 O added. I learned that dmso peak in 1H NMR caused by proton exchange. Pure deuterated DMSO shows no peaks in H NMR spectroscopy and as a result is commonly used as an NMR solvent. Except where indicated, the coupling constants, and therefore the peak shapes, are essentially solvent-independent and are presented only once. the NMR tube. In less than 95% deuterated DMSO you can also spot d4 signal as a small shoulder on the left side of the DMSO quintet. it is d5. Note the reduced ratio of the phenolic proton 18:3:2:0.47 (t-butyl: methyl: ring-H: -OH). Why does the water peak appear at different chemical shift values (ppm) in different solvents in proton NMR spectra?