Which of the following solvents are appropriate for NMR spectroscopy? Why?

Question

Acetone
Water
Benzene-d6
#CDCl_3#
#CF_3OOH#
Dioxane-d8

Christian Anderson · Accepted Answer

Only the deutero-solvents are suitable for #""^1H# #"NMR spectroscopy"#.

When #""^1H# #NMR# experiments are performed, the diamagnetism of all #""^1H# nuclei in the SAMPLE are interrogated. If we use solvents that already contain #""^1H#, then these signals WiLL DOMINATE the spectrum. (Why? because of their concentration.) Sometimes, a solvent can be used that contains few #""^1H# nuclei, i.e. per-fluoroacetic acid. The chemical shift of the proton here would occur well downfield, leaving a window for the desired spectrum. The deuterium signal is also used by contemporary NMR spectrometers to lock the frequency (the deuterium frequency serves as the reference frequency; keep in mind, though, that spectra are frequently run unlocked these days due to the tendency of magnetic fields to be very stable). Of course, #""^31P# and #""^11B# NMR spectroscopies are now routinely performed. Researchers in these fields often add a small quantity of deutero solvent to their reaction mixture, and do the experiment for the heteroatom (in which the proton resonance will be invisible, why?). Deutero solvents (apart from chloroform-d) tend to be horrendously expensive, and the more expensive ones (i.e. #"toluene"-d_8#, #"methylene chloride"-d_2#, #"THF"-d_8#, #"benzene"-d_6#) tend to collected after an experiment, and then recycled by distillation (which of course is a very good practice both in terms of economy and the environment).

Ella Allen · Answer

undefined Common solvents used in NMR spectroscopy include deuterated solvents such as chloroform (CDCl3), deuterated dimethyl sulfoxide (DMSO-d6), deuterated methanol (CD3OD), deuterated acetone (CD3COCD3), and deuterated water (D2O). These solvents are chosen because they are inert, do not interfere with the sample, and have a low signal in the NMR spectrum, allowing for clear detection of the sample signals.

Which of the following solvents are appropriate for NMR spectroscopy? Why?

Acetone Water Benzene-d6 #CDCl_3# #CF_3OOH# Dioxane-d8

Acetone
Water
Benzene-d6
#CDCl_3#
#CF_3OOH#
Dioxane-d8