When a substance such as ethanol, \(CH_3-CH_2-OH\), the hydrogens of which have nuclei (protons) that are magnetic, is placed in the transmitter coil and the magnetic field is increased gradually, at certain field strengths radio-frequency energy is absorbed by the sample and the ammeter indicates an increase in the flow of current in the coil. The arrows through the nuclei represent the average component of their nuclear magnetic moment in the field direction.Ī schematic diagram of an NMR instrument is shown in Figure 9-22. Transitions between the two states constitute the phenomenon of nuclear magnetic resonance. Figure 9-21: Schematic representation of the possible alignments of a magnetic nucleus (here hydrogen) in an applied magnetic field. The two orientations are not equivalent, and energy is required to change the more stable alignment to the less stable alignment. The nuclear magnets can be aligned either with the field direction, or opposed to it. There are two possible alignments of this magnetic nucleus with respect to the direction of the applied field, as shown in Figure 9-21. To illustrate the procedure with a simple example, consider the behavior of a proton \(\left( ^1H \right)\) in a magnetic field. In NMR spectroscopy, we measure the energy required to change the alignment of magnetic nuclei in a magnetic field. The nuclei of many kinds of atoms act like tiny magnets and tend to become aligned in a magnetic field. The principle on which this form of spectroscopy is based is simple. Nuclear magnetic resonance (NMR) spectroscopy is extremely useful for identification and analysis of organic compounds.
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