Physics : Nuclear Magnetic Resonance

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Introduction Nuclear magnetic resonance (NMR) spectroscopy and imaging are very useful tools that have practical applications for several different fields. Chemists can use NMR spectroscopy to determine the structure and composition of organic molecules. NMR imaging is used in the field of medicine to view detailed cross-sectional slices of the human body. NMR is used by the petroleum industry as well as the pharmaceutical industry. This report examines how NMR spectroscopy is used to determine the structure of an unknown organic molecule. Methods This methods section will explain the theory behind NMR spectroscopy. NMR spectroscopy is achieved by using electromagnetic fields to manipulate the spin of protons or nuclei within a molecule1. The state of spin describes the proton’s or nuclei’s orientation in space2. In 1H and 13C atoms the nuclei spin behaves like small magnets. In a 1H atom a proton can possess one of two spin states, -1/2 or +1/2. Normally the spin orientation of nuclei is random but because the nuclei have a magnetic moment the spin can be quantized by an external magnetic field2. In the presence of a very strong magnet, 1-20 tesla, the protons will align themselves with or against the magnetic field depending on their spin state1. The magnetic field produces a measurable difference in energy between the two spin states. With no magnetic field present the energy difference between the two spin states is zero. The energy difference between the two spin states
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