Current Model: Bruker Avance 400MHz spectrometer.
Typical samples: Organic compounds, polymers, sol gels.
Typical Analysis Steps: 1.Sample is dissolved in an appropriate deuterated solvent 2.Sample is placed in an NMR tube 3.Experiment is run (either automatically or manually) and raw data is converted to a spectrum for analysis.
NMR spectroscopy operates on the principle that when certain atomic nuclei (atoms that make up molecules) are exposed to a magnetic field they absorb and re-emit electromagnetic (EM) radiation. This method is theoretically applicable to any nuclei that have an intrinsic magnetic moment such as 1H, 13C, 15N, 19F and 29Si. The frequency of the emitted EM radiation depends on the specific nuclei and more importantly the specific chemical environment it is in. By chemical environment we mean what atoms are bonded directly to the nuclei under study and what atoms are bonded to them and so on. This is important because it will determine where the electrons are in the molecule.
If you consider the molecule butanal shown below the right side has no significantly electronegative atoms (only hydrogen and carbon) so the electrons will be quite evenly distributed, hence the 1H nuclei are considered ‘shielded’. If you look at the left side of the molecule the circled hydrogen atom is bonded to a carbonyl group (C=O). The oxygen atom is very electronegative so it will pull electron density away from the hydrogen atom in question. This hydrogen nuclei is then considered to be ‘de-shielded’. The significance of this is that the shielded nuclei emit lower frequency EM radiation than the de-shielded nuclei. This effect will then allow you to elucidate the structure of different molecules as demonstrated by the 1H NMR spectrum shown.
The splitting of the signals and their intensities also provide additional information about the chemical structure.