Basic Operation The instructor demonstrates the basic operation of the spectrometer, on a standard sample. This will be followed by individual trainings in which you will run your own samples, with the help of the Teaching Assistant. Most people need three individual sessions, but take as many sessions as needed until you feel confident.
Variable Temperature Lowering the temperature can reveal individual spectra for species which at room temperature are in fast exchange, and display a single set of signals, possibly broad signals, for all of the species. Conversely, raising the temperature will simplify spectra of amides. One might need to run spectra at higher temperature to improve the solubility.
Other Nuclei Most of the elements have NMR active isotopes, which can give insight on the structure. Isotopes with spin ½, high natural abundance and higher frequency are preferred, but H2, Li6, Li7, B11 or Al27 are easy to observe as well. For a quick look at the receptivity of other isotopes click here. This training deals with direct observation of these nuclei; for indirect detection, as for N15 at natural abundance, take the 2D training.
Solvent suppression For samples of peptides, which are run in 10 % D2O in H2O, to prevent deuteration of the amide protons, solvent suppression is a must. One can check reactions directly, without the need to evaporate the solvent and re-dissolve in a deuterated one, by suppressing the solvent signals, FID shimming and running without lock. As many signals as desired can be suppressed.
Selective excitation 1D experiments TOCSY1D reveals the protons in the same coupling network with the excited one; it is a very useful experiment for identifying compounds in a reaction mixture. Other experiments reveal the protons which have an nOe with the excited one, and offer thus a quick solution to stereochemical problems.
2D NMR allows for structure elucidation by correlations of H1 and C13 chemical shifts. Common experiments are:
gDQCOSY – cross-peaks between the frequencies of the protons which couple with each other.
TOCSY – cross-peaks between the frequencies of the protons which are in the same coupling network.
gHSQC – cross-peaks between the frequencies of the protons and carbons one bond away.
gHMBC – cross-peaks between the frequencies of the protons and carbons two or three bonds away. This experiment is the bread-and-butter of structure elucidation, since it reveals the hydrocarbon skeleton of a molecule. Consider running a gHMBC instead of a C13 spectrum, since it has better sensitivity, up to 32 times, and also offers the correlation information.
NOESY/ROESY – cross-peaks between the frequencies of the protons which have an nOe, or are in exchange.here). Request a training manual