Some atomic nuclei have a magnetic moment a randomly-distributed spin that can be either +1/2 or -1/2. In Nuclear Magnetic Resonance (NMR) Spectroscopy, a sample (usually containing hydrogen or the carbon-13 isotope) is exposed to a superconducting magnet. Most of the spins will align with the magnet, because that is the lowest energy state. When exposed to radiofrequency energy, which can be absorbed by the nuclei to flip the nuclear spin so it is opposed to the magnetic field. Each absorbed energy corresponds to a different nucleus, indicating which ones are present in the sample. The structure and splitting of the peaks indicates neighboring groups and their environment. Molecular symmetry plays a big role in predicting and interpreting NMR spectra, as does the n+1 rule. The height of each peak (corrected) can indicate how many of each type of nucleus is present, so integral trails are often included. Chemical shift (delta) corresponds to whether a given nucleus is electron-rich or electron-poor.
Nuclear Magnetic Resonance (NMR) Spectroscopy, Part I
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