#""^1H# and #""^13C{""^1H}# #"NMR spectroscopies"# remain a direct and very powerful tool of analysis for observation and identification of organic species in solution. As with any form of spectroscopy, a standard is usually used to calibrate the observed spectrum, so the measurement can be repeated and verified on different instruments.
This is typically the residual proton residue of the deuterated solvent that is used to acquire the spectrum (i.e. because we typically want to observe protons, we use a solvent such as #d-"chloroform"# or #d_6-"benzene"#, i.e. #C""^2HCl_3# or #C_6""^2H_6#; because these so-called deuterated solvents contain NEXT to NO protons, i.e. #""^1H# #"nuclei"#, they are transparent in the #""^1H# #"NMR"# spectrum of the sample.
The residual protons in the sample (rarely can we afford to use 100% deuterated solvents) act as an internal reference with which we can calibrate the observed #""^1H# #"NMR spectrum"#.
And thus in the #""^1H# #"NMR spectrum"#, we have an internal standard; i.e. residual #""^1H# resonances of the solvent; i.e. #C_6D_5H=7.15*"ppm"#; #CD_2HCl=7.24*"ppm"#; #C_6D_5CD_2H=2.15*"ppm"#. These chemical shifts are ALL with respect to #delta=0*"ppm"# for the equivalent methyl protons in #(H_3C)_4Si#. And thus we can precisely and #"internally"# calibrate the observed spectrum.
The use of deuterons rather than protons, is important in another respect. Modern NMR spectrometers usually have THREE channels: #(i)# for observing #""^1H# nuclei; #(ii)# for observing heteroatoms, i.e. #""^13C#, #""^31P#, #""^15N#, which occur at frequencies to which the spectrometer can conveniently be tuned; and #(iii)# the #"deuterium"# or locking channel. The spectrometer can detect absorptions of #""^2H# nuclei, and measurement can be calibrated by #"locking"# onto this channel. The use of deuterium in labelling experiments given an active hydrogen (i.e. one that can exchange protons for deuterons) is also widespread.
I am told these days, the modern operators sometimes do not even bother to use the locking channel. The magnetic fields generated are so stable, that they do not vary so much, and #""^1H# spectra can often be run #"unlocked"# (and even without spinning the sample!). Anyway, all of this should be known by a second year or third year organic student. At A-level you should know that #""^1H# and #""^13C{""^1H}# #"NMR spectroscopy"# are a very powerful and direct means to characterize organic compounds in real time in solution.
