Proton environment spectroscopy

Sposito, G., Schaumberg, G. D., Perkins, T. G., and Holtzclaw, K. M. (1978). Investigation of fulvic acid extracted from sewage sludge using carbon-13 and proton NMR spectroscopy. Environ. Sci. Technol 12, 931-934. 

Proton NMR spectroscopy is particularly useful for determining the disposition of substituents in aminohalogenocyclophosphazenes. Four criteria are utilized for this purpose (a) the number of proton environments, (b) the value of 3J (P—H), (c) the relative chemical shifts (geminal versus nongeminal and cis versus trans), and (d) the presence or absence of "virtual coupling (see detailed discussion in the following). 

New possibilities for such purity examinations have opened up with the development of C-resonance spectroscopy. By means of this method it is now possible to distinguish between carbon atoms in different chemical environments. In accordance with the above considerations, this may be utilized for qualitative investigations. It should be noted, however, that the sensitivity of the carbon-resonance method is lower than that of proton-resonance spectroscopy. Owing to the low abundance of the isotope, the measurements must be carried out in more concentrated solutions. At the same time, the resolution of carbon-resonance spectroscopy is higher than that of proton-resonance spectroscopy, hence the former can be used for the detection of impurities (when present in sufficiently high... 

One property of NMR spectroscopy is that it is too slow a technique to see the mdi vidual conformations of cyclohexane What NMR sees is the average environment of the protons Because chair-chair mterconversion m cyclohexane converts each axial pro ton to an equatorial one and vice versa the average environments of all the protons are the same A single peak is observed that has a chemical shift midway between the true chemical shifts of the axial and the equatorial protons... 

The information derived from 13C NMR spectroscopy is extraordinarily useful foT structure determination. Not only can we count the number of nonequivalent carbon atoms in a molecule, we can also get information about the electronic environment of each carbon and can even find how many protons each is attached to. As a result, we can answer many structural questions that go unanswered by TR spectroscopy or mass spectrometry. 

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