6A_Lecture_6_with_ink

6A_Lecture_6_with_ink - Lecture 6 Nuclear Magnetic...

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Lecture 6
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Nuclear Magnetic Resonance Experiment 6
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Infrared Spectroscopy gives Functional Group Information only How do you tell these two molecules apart?
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Methyl propanoate vs. Ethyl acetate
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Nuclear Magnetic Resonance (NMR) MRI
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Concept first reported in 1938 Felix Bloch (top) and Ed Purcell applied concept to 1H and 31P They noticed these nuclei absorbed RF energy when put in a magnetic field Shared 1952 Nobel Prize in physics Has been used since to elucidate the chemical structures of compounds Preeminent form of spectroscopy
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How does NMR work? Foundation of NMR is nuclear spin ( I ) I is related to atomic number and mass number Nuclei with I > 0 can theoretically be detected Simplest spin number to understand is 1/2
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1H and 13C nuclei have spin of ½ Spin states can be inverted with RF energy by placing in a strong magnetic field
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There is a change in energy between the spin states. It increases with the field strength of the magnet.
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Isotope Natural % Abundance Spin (I) Magnetic Moment (μ)* 1 H 99.98 ½ 2.7927 2 H 0.015 1 0.8574 19 F 100 1/2 2.6273 13 C 1.11 ½ 0.7022 12 C 98.99 0 16 O 99.76 0
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NMR is low-energy and non-destructive to the sample. This is why humans can be samples (MRI)
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How is the 1H signal detected then?? Sample is irradiated with RF energy as the Magnetic Field is varied When the RF energy equals the energy of the magnetic field, a resonance occurs and this is seen as a signal
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Why should 1H nuclei of different compounds
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6A_Lecture_6_with_ink - Lecture 6 Nuclear Magnetic...

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